Rodak's Hematology: Clinical Principles and Applications, 5th Ed.


a-β-lipoproteinemia  Autosomal recessive disorder of lipoprotein metabolism in which lipoproteins containing apolipoprotein B (chylomicrons, very-low-density lipoproteins, and low-density lipoproteins) are not synthesized. Characterized by the presence of peripheral blood film acanthocytes and low plasma cholesterol levels.

absolute neutrophil count (ANC)  Total of neutrophils per liter of blood. The absolute neutrophil count is calculated by multiplying the total white blood cell count by the percentage of segmented neutrophils and bands or may be counted directly using an automated hematology analyzer.

absolute reticulocyte count (ARC)  Reticulocytes per liter. The absolute reticulocyte count is calculated by multiplying the patient’s visual reticulocyte count (reticulocyte percentage, VRET%) by the red blood cell count or may be measured directly using an automated hematology analyzer.

acanthocyte  Red blood cell with spiny projections of varying lengths distributed irregularly over its surface, associated with lipid imbalance. Contrast with the echinocyte, which has regular projections of uniform length.

acanthocytosis  Presence of acanthocytes in the blood. Associated with abetalipoproteinemia or abnormalities of lipid metabolism, such as abnormalities occurring in liver disease.

accuracy  Extent to which an assay result matches its true value. Accuracy is computed by comparing assay results with the results from an established reference assay or a primary standard.

achlorhydria  Pathologic absence of free hydrochloric acid from gastric secretions following stimulation.

acid elution slide test (Kleihauer-Betke stain)  Test for detecting fetal red blood cells (RBCs) in the maternal circulation. Blood films are immersed in an acid buffer, which causes adult hemoglobin (Hb A) to be eluted from RBCs. The film is stained, and RBCs that have fetal hemoglobin (Hb F) take up the stain.

acquired immunodeficiency syndrome (AIDS)  Late-stage immune system suppression characterized by depletion of CD4+ T lymphocytes and depression of cellular immunity causing susceptibility to opportunistic infections and neoplasms. Caused by infection with human immunodeficiency virus (HIV), a retrovirus.

acrocentric  Describes the appearance of a metaphase chromosome with the centromere near one end, which causes the q arm to be much longer than the p arm.

acrocyanosis (Raynaud phenomenon)  Persistent symmetrical cyanosis (blotchy blue or red discoloration) in the skin of the digits, palm, wrists, and ankles, and less frequently the nose and ears, upon prolonged exposure to cold.

activated coagulation time (ACT)  Whole-blood clotting time test often used in cardiac surgical suites. A particulate activator is added to blood, the mixture is rocked, and the interval to clotting is recorded. Employed to monitor high-dose unfractionated heparin therapy during cardiac catheterization or coronary artery bypass graft surgery.

activated partial thromboplastin time (APTT, partial thromboplastin time, PTT)  Clot-based screening test for intrinsic coagulation that is prolonged in deficiencies of prekallikrein, high-molecular-weight kininogen, factors XII, XI, IX, VIII, X, V, and II (prothrombin), and fibrinogen. Calcium chloride, phospholipid, and negatively charged particulate activator are added to patient plasma. The interval from the addition of reagent to clot formation is recorded. The test is used to monitor unfractionated heparin therapy and to screen for intrinsic and common pathway deficiencies, specific factor inhibitors, and lupus anticoagulant.

activated protein C (APC)  Coagulation pathway regulatory protein activated by the thrombin-thrombomodulin complex that, when bound and stabilized by protein S, hydrolyzes and inactivates factor Va and factor VIIIa.

activated protein C resistance (APCR)  Inherited condition in which activated coagulation factor V (Va) resists activated protein C digestion, which results in an increased risk of venous thrombosis. In 90% of cases, activated protein C resistance is caused by the factor V Leiden mutation.

activated prothrombin complex concentrate  Therapeutic plasma preparation that bypasses factor VIII activation, used to treat bleeding episodes in hemophilic patients who have developed factor VIII inhibitor. Contains activated factors II (prothrombin), VII, IX, and X. Also known as prothrombin complex concentrate, factor eight inhibitor bypassing activity (FEIBA; Baxter Healthcare Corporation, Deerfield, IL).

acute  Describes diseases whose symptoms begin abruptly with marked intensity and then subside after a relatively short period.

acute leukemia  Malignant, unregulated proliferation of hematopoietic progenitors of the myeloid or lymphoid cell lines. Characterized by abrupt onset of symptoms and, if left untreated, death within months of the time of diagnosis.

acute myocardial infarction (AMI)  Occlusion of a coronary artery by a clot, causing ischemia and necrosis (tissue death) of surrounding heart muscle. Commonly called a heart attack.

acute phase reactant  Serum protein produced by the liver whose level rises during inflammation. Examples include C-reactive protein, ferritin, and fibrinogen.

adenopathy  Enlargement of one or more lymph nodes.

adenosine diphosphate (ADP)  Purine nucleotide that activates platelets by binding platelet receptor P2Y1 and P2Y12. Produced by hydrolysis of adenosine triphosphate.

adenosine triphosphate (ATP)  Purine nucleotide that stores energy in the form of high-energy phosphate bonds, releasing energy upon hydrolysis to drive metabolic reactions.

adhesion  Property of binding or remaining in proximity; for example, attachment of platelets to surfaces such as subendothelial collagen.

adipocyte  Fat cell; adipocytes make up adipose tissue and the yellow portion of the bone marrow.

afibrinogenemia  Complete absence of plasma fibrinogen.

agammaglobulinemia  Immunodeficiency characterized by an absence or extremely reduced level of plasma gamma globulin and reduced levels of immunoglobulins. Associated with increased risk of infection.

agglutination  Cross-linking of antigen-bearing cells or particles by a specific antibody to form visible clumps.

aggregation  Cluster or clump of similar cell types or particles; for example, attachment of platelets to other platelets, red blood cell clumping.

agnogenic  Of idiopathic or unknown origin.

agranulocytosis  Any condition involving decreased numbers of granulocytes (segmented neutrophils or band neutrophils).

albinism  Hereditary condition characterized by partial or total lack of melanin pigment in the body; skin, hair, and eyes may be affected. Individuals with total albinism have pale skin that does not tan, white hair, and pink eyes. Albinism is often associated with platelet storage pool deficiency.

Alder-Reilly anomaly  Autosomal dominant polysaccharide metabolism disorder in which white blood cells (WBCs) of the myelocytic series, and sometimes all WBCs, contain coarse azurophilic mucopolysaccharide granules.

allele  One of two or more alternative forms of a gene that occupy corresponding loci on homologous chromosomes. Each allele encodes a certain inherited characteristic. An individual normally has two alleles for each gene, one contributed by the mother and one by the father. If both alleles are the same, the individual is homozygous, but if the alleles are different, the individual is heterozygous. In heterozygous individuals, one of the alleles may be dominant and the other recessive.

alloantibody (isoantibody)  Antibody that is produced in response to the presence of foreign antigens; for instance, an antibody to a therapeutic coagulation factor that may render factor therapy ineffective.

alloimmune  Producing antibodies to antigens derived from a genetically dissimilar individual of the same species.

alloimmune hemolytic anemia  Anemia caused by antibodies stimulated by exposure to foreign red blood cell (RBC) antigens. Antibodies coat and shorten the life span of circulating RBCs. This is the basis for hemolytic disease of the newborn.

α-granules  Platelet granules that store and release a variety of hemostasis proteins. There are 50 to 80 α-granules per platelet. In transmission electron microscopy, α-granules appear light gray, in contrast to δ-granules (dense bodies), which appear black.

α-thalassemia  Moderate to severe inherited anemia caused by a decreased or absent production of the α-globin chains of hemoglobin.

amyloidosis  Disease in which a waxy, starchlike glycoprotein (amyloid) accumulates in tissues and organs, impairing their function.

analogue drugs  Drugs that are chemically similar to one another but, because of minor structural differences, may have different physiologic actions.

anaplastic  Characterized by loss of differentiation and growth without structure or form. Anaplasia is a characteristic of cancer.

anatomic bleeding disorder  Chronic episodic bleeding into soft tissue, joints, and body cavities. Indicates a secondary coagulopathy such as hemophilia or an acquired coagulation factor deficiency.

anemia  Diminished delivery of oxygen to tissues, as evidenced by pallor, malaise, and dyspnea. May be caused by blood loss, decreased red blood cell (RBC) production, increased RBC destruction (shortened life span).

aneuploid  Having a chromosome number that is not an exact multiple of the normal diploid number (46 in humans) so that there are fewer or more chromosomes than normal.

anisocytosis  Abnormal red blood cell (RBC) morphology characterized by considerable variation in RBC volume or RBC diameter on a blood film.

annular diaphragm  Device used in phase microscopy that, together with a phase-shifting element, produces contrast between an unstained cell and its dark background.

anoxia  Inadequate tissue oxygenation caused by poor lung perfusion or a diminished blood supply.

antagonist  Drug that nullifies the action of another drug or that reduces a normal cellular response. Aspirin is a platelet antagonist because it reduces platelet activation.

antecubital fossa  Concavity opposite the elbow.

antibody (Ab)  Specialized protein (immunoglobulin) that is produced by B lymphocytes and plasma cells when the immune system is exposed to foreign antigens from bacteria, viruses, or other biologic materials. An antibody molecule has a specific amino acid sequence in its variable region that matches it to the antigen that originally stimulated its production.

anticardiolipin antibody (ACL, ACA)  Member of the antiphospholipid antibody family that includes anti–β2-glycoprotein 1 and lupus anticoagulant. An ACL antibody is an autoantibody detected in a solid-phase immunoassay system using cardiolipin as the target antigen. The chronic presence of ACL antibodies is associated with venous and arterial thrombotic disease.

anticoagulant  Therapeutic agent that delays blood coagulation, such as heparin or warfarin, used to prevent thrombotic events in patients who are at risk. Additive to blood specimen collection tubes that prevents in vitro blood clotting such as sodium citrate.

antigen  Molecule that the immune system recognizes as foreign and that subsequently evokes an immune response.

antihemophilic factor (AHF)  Therapeutic concentration of coagulation factor VIII produced through chemical fractionation, immunoaffinity column, or recombinant synthesis. Antihemophilic factor is prescribed in the treatment of hemophilia A, a hereditary deficiency of factor VIII.

antineoplastic  Chemotherapeutic agent that controls or kills cancer cells.

antiphospholipid antibody (APL, APA)  Member of the antibody family that includes anticardiolipin, anti–β2-glycoprotein I, and lupus anticoagulant. APL antibodies bind phospholipid-binding proteins, such as β2-glycoprotein. The presence of an APL antibody is associated with venous and arterial thrombotic disease.

antiphospholipid syndrome (APS)  Group of thrombotic disorders related to the chronic presence of an antiphospholipid antibody, such as anticardiolipin, anti–β2-glycoprotein I, or lupus anticoagulant. Manifestations include migraine, transient ischemic attacks, strokes, acute myocardial infarction, peripheral artery disease, venous thromboembolic disease, and spontaneous abortion.

antithrombin (AT, antithrombin III, AT III)  Plasma serine protease inhibitor produced in the liver and activated by therapeutic heparin or vascular heparan sulfate. When activated, antithrombin controls the coagulation pathway, because it neutralizes all the serine proteases except factor VIIa, most importantly factors IIa (thrombin) and Xa.

aperture  Optical device in a microscope substage light path that controls the diameter of the light column that reaches the specimen. The aperture may be adjusted to improve specimen clarity.

aplasia  Failure of the normal process of cell generation and development. Bone marrow aplasia is the loss of all bone marrow cellular elements.

aplastic anemia  Deficiency of all of the formed elements of blood, representing a failure of the blood cell–generating capacity of bone marrow.

apoferritin  Protein component of the ferritin molecule consisting of 24 identical spherical subunits that surround iron in the ferric valence form.

apoptosis  Natural cell death characterized by nuclear condensation and loss of cytoplasmic integrity. Apoptosis is a mechanism that prevents proliferation of dysplastic or mutated cells.

aspirin (acetylsalicylic acid, ASA)  Acetylsalicylic acid in tablet form; irreversibly acetylates platelet cyclooxygenase and reduces platelet activation. Aspirin is used for its antithrombotic properties.

asynchrony  Disturbance of coordination that causes processes to occur at abnormal times. In hematopoietic cell development, a difference in rate between cytoplasmic and nuclear maturation.

atrial fibrillation (AFIB)  Uncontrolled and ineffective atrial heartbeat that affects at least 2 million U.S. citizens. Atrial fibrillation raises the risk for stroke. The risk is controlled using long-term anticoagulation therapy, such as warfarin.

atypical lymphocytes (transformed, reactive, or variant lymphocytes)  Lymphocytes whose altered morphology includes stormy blue cytoplasm and lobular or irregular nuclei. Variant lymphocytes indicate stimulation by a virus, particularly Epstein-Barr virus, which causes infectious mononucleosis.

Auer rod  Abnormal needle-shaped or round pink to purple inclusion in the cytoplasm of myeloblasts and promyelocytes; composed of condensed primary granules. Indicates acute myeloid leukemia.

autoantibody  Antibody produced by an individual that recognizes and binds an antigen on the individual’s own tissues.

autoimmune  Describes an immune response in which an antibody forms to one’s own tissues; for instance, antinuclear antibody in lupus erythematosus.

autoimmune hemolytic anemia  Anemia characterized by premature red blood cell (RBC) destruction. Autoantibodies to RBC surface antigens bind the membrane, causing rapid splenic clearance and hemolysis.

autologous  Related to self or belonging to the same organism; for example, used to describe blood that is donated by patients before surgery for the purpose of transfusion to themselves during or after surgery.

autosomal dominant inheritance  Pattern of inheritance in which the transmission of a dominant allele on an autosome causes a trait to be expressed in heterozygotes.

autosomal inheritance  Inheritance of traits located on non–sex-related chromosomes.

autosomal recessive inheritance  Pattern of inheritance resulting from the transmission of a recessive allele that is not expressed in heterozygotes.

autosome  Any of the 22 pairs of chromosomes in humans other than the sex chromosomes X and Y.

autosplenectomy  Disappearance of the spleen through progressive fibrosis and shrinkage secondary to a hemolytic anemia such as sickle cell anemia.

azurophilic  Having cellular structures that stain blue with Giemsa stain and red-purple with Wright stain.

azurophilic granules  Primary cytoplasmic granules in myelocytic cells that, when stained with Wright stain, appear reddish purple. Azurophilic granules of different composition may also appear in a minority of lymphocytes.

B cell  Any of a family of lymphocytes that produce antibodies. The end product of B-cell maturation is the plasma cell.

Babesia  Protozoal parasite transmitted by ticks that infects human red blood cells and causes babesiosis, a malaria-like illness. The parasite is an intracellular ringlike structure 2 to 3 µm in diameter.

band neutrophil (band)  Immediate precursor of the mature segmented neutrophil. Band neutrophils have a nonsegmented, usually curved, nucleus and are present in the bone marrow and peripheral blood.

bartonellosis  Acute febrile infection caused by the bacterium Bartonella bacilliformis, which is transmitted by the bite of a sandfly. The first stage of the disease is associated with severe hemolytic anemia.

base pair  Pair of nucleotides in the complementary strands of a DNA molecule that interact through hydrogen bonding across the axis of the DNA helix. One of the nucleotides in each pair is a purine (either adenine or guanine), and the other is a pyrimidine (either thymine or cytosine). Adenine always pairs with thymine, and guanine always pairs with cytosine.

basophil (baso)  Granulocytic white blood cell characterized by cytoplasmic granules that stain bluish black when exposed to a basic dye. Cytoplasmic granules of basophils are of variable size and may obscure the nucleus.

basophilia  Abnormal increase of basophils in the blood.

basophilic normoblast (prorubricyte)  Second identifiable stage in bone marrow erythrocytic maturation; it is derived from the pronormoblast (rubriblast). Typically 10 to 15 µm in diameter, the basophilic normoblast (prorubricyte) has cytoplasm that stains dark blue with Wright stain.

basophilic stippling  Barely visible dark blue to purple granules evenly distributed within a red blood cell stained with Wright stain. Composed of precipitated ribosomal protein and RNA.

Bence Jones protein  Protein found almost exclusively in the urine of patients with multiple myeloma, consisting of the light chain of the abnormal immunoglobulins produced.

benign  Noncancerous or nonmalignant.

Bernard-Soulier syndrome (BSS)  Mild to moderate mucocutaneous bleeding disorder caused by one of a series of mutations to platelet glycoprotein Ib (GP Ib) or GP IX, part of the GP Ib/IX/V von Willebrand factor receptor complex. The disorder is a defect of platelet adhesion.

β2-glycoprotein I (β2-GPI)  Plasma globulin that is a target of the antiphospholipid antibody anti–β2-glycoprotein I.

β-thalassemia  Inherited anemia caused by diminished synthesis of the β-globin chains of hemoglobin.

β-thromboglobulin (β-TG)  Heparin-neutralizing protein that is stored and secreted by platelet α-granules.

bilirubin  Gold-red-brown pigment, the main component of bile and a major metabolic product of the heme portion of hemoglobin, released from senescent red blood cells. Elevated bilirubin imparts a gold color to plasma and urine and may indicate hemolytic anemia, liver disease, or bile duct occlusion.

bilirubinemia (icterus, hyperbilirubinemia)  Excess bilirubin in plasma. It imparts a gold color to plasma and may indicate hemolytic anemia, liver disease, or bile duct occlusion.

2, 3-bisphosphoglycerate (2, 3-BPG, 2, 3-diphosphoglycerate, 2, 3-DPG)  Product of red blood cell glycolysis that is generated in the Rapoport-Luebering shunt. 2, 3-BPG is one of the main regulators of oxygen uptake and delivery by hemoglobin. 2, 3-BPG decreases hemoglobin’s affinity for oxygen, which enables it to more readily release oxygen to the target tissues.

blast  Earliest, least differentiated stage of hematopoietic maturation that can be identified by its morphology in a Wright-stained bone marrow smear; for example, myeloblast, pronormoblast (rubriblast), lymphoblast.

bleeding time (BT)  Time interval required for blood to stop flowing from a puncture wound 2 mm long and 1 mm deep on the volar surface of the forearm. Largely of historical interest, the bleeding time test was performed to evaluate vascular and platelet function.

Bohr effect  Effect of carbon dioxide and hydrogen ions on the affinity of hemoglobin for oxygen. Increasing carbon dioxide and hydrogen ion concentrations (lower pH) decrease oxygen saturation; decreasing concentrations increase oxygen saturation.

bone marrow  Gelatinous red and yellow tissue filling the medullary cavities of bones. Red marrow is found in most bones of infants and children and in the ends of long bones and the cavities of flat bones in adults. Diagnostic marrow specimens are collected from the anterior or posterior iliac crest or sternum in adults. Fatty yellow marrow is found in the medullary cavity of most adult long bones.

bone marrow aspirate specimen  A 1- to 1.5-mL aliquot of gelatinous red marrow obtained by passing a needle into the marrow cavity and applying negative pressure. The aspirate specimen is spread as a smear on a microscope slide, stained, and examined for hematologic or systemic disease. The aspirate specimen provides for analysis of individual cell morphology.

bone marrow biopsy specimen  A 1- to 2-cm cylinder of gelatinous red marrow obtained by passing a biopsy cannula into the marrow cavity, rotating, and withdrawing. The cylinder is fixed in formalin, sectioned, stained, and examined for hematologic or systemic disease. The biopsy specimen provides for analysis of bone marrow architecture.

buffy coat  Gray-white layer of white blood cells (WBCs) and platelets that accumulates at the red blood cell–plasma interface when a tube of anticoagulated blood is allowed to stand or is centrifuged. The buffy coat may be used to harvest WBCs for microscopic analysis when the WBC count is low, and an enlarged buffy coat may indicate leukemia.

Burkitt lymphoma  Lymphatic solid tissue tumor composed of mature B lymphocytes with a characteristic morphology, called Burkitt cells. Burkitt cells appear in lymph node biopsies, bone marrow, and occasionally in peripheral blood and have dark blue cytoplasm with multiple vacuoles creating a “starry sky” pattern.

burst-forming unit (BFU)  Early hematopoietic progenitor cell stages of the erythroid and megakaryocytic cell lines characterized by their tissue culture growth pattern in which large colonies are produced. Contrast with the more differentiated colony-forming units, which produce smaller colonies.

C banding  In cytogenetic analysis, a specialized Giemsa stain technique employing first an acid and then a basic buffer, which highlights the centromeres of chromosomes. The stained centromere is the C band, which helps to identify the chromosome.

Cabot rings  Threadlike structures that appear as purple-blue loops or rings in Wright-stained red blood cell cytoplasm. They are remnants of mitotic spindle fibers that indicate hematologic disease such as megaloblastic or refractory anemia.

calibrator (secondary standard)  Preserved material in which the analyte concentration has been assigned by reference to a primary standard or by controlled reference assays in expert laboratories. Calibrators are used for assays in which there are no primary standards, such as blood cell counts or coagulation assays.

carboxyhemoglobin  Hemoglobin that has bound carbon monoxide, which prevents normal oxygen exchange. Carboxyhemoglobin imparts a cherry-red color to venous blood, and its reduced oxygen capacity is the basis for carbon monoxide poisoning.

carcinoma  Malignant neoplasm of epithelial cell origin that invades surrounding tissue and may metastasize to distant regions of the body.

cell membrane  Cell surface composed of two layers of phospholipids intermixed with cholesterol and a variety of specialized glycoproteins that support cell structure, signaling, and ion transport.

cellular immunity (cell-mediated immunity, CMI)  Immune response initiated and mediated by T-lymphocyte secretions called cytokines, natural killer cells, and macrophages; the mechanism of acquired immunity characterized by the dominant role of the T lymphocytes. Cellular immunity is the basis for graft rejection, delayed hypersensitivity, and responses to viral infections and tumors.

centriole  Cylindrical organelle composed of microtubules. Two centrioles typically orient perpendicular to each other forming the centrosome, located near the nucleus. During mitosis they replicate and move to opposite ends of the cell where they bind to spindle fibers that attach to the centromeres of chromosomes and effect their movement during metaphase.

centromere  Constricted portion of a chromosome that attaches to a spindle fiber to effect movement during metaphase. Centromeres are categorized by their location as acrocentric (near one end), metacentric (near the center), or submetacentric (off center).

cerebrospinal fluid (CSF)  Fluid that flows through and protects the four ventricles of the brain, the subarachnoid spaces, and the spinal canal. CSF is derived from plasma and is the site of bacterial and viral infections called meningitis or encephalitis. CSF is sampled by lumbar puncture.

cerebrovascular accident (CVA)  Stroke; occlusion of an artery of the brain or brain hemorrhage resulting in necrosis of brain tissue and loss of function.

Charcot-Leyden crystals  Crystalline structures that are shaped like narrow double pyramids and are found in the sputum of asthma patients and the feces of dysentery patients. Formed from the granules of disintegrating eosinophils.

Chédiak-Higashi anomaly  Autosomal recessive disorder characterized by partial albinism, photophobia, susceptibility to infection, and the presence of giant blue granules in the cytoplasm of Wright-stained white blood cells and platelets.

chelation  Chemical formation of a ring-shaped molecular complex in which a metal ion is covalently bound. Chelating agents such as ethylenediaminetetraacetic acid (EDTA) or sodium citrate trap calcium ions and are used as blood specimen anticoagulants. Chelators are also used to treat lead poisoning or iron overload.

chemotaxis  Cellular movement toward or away from a chemical stimulus. Characteristic of neutrophils and monocytes, whose phagocytic activity is influenced by chemical factors released by invading microorganisms.

chemotherapy  Treatment of neoplastic disease (cancer) by chemical agents.

chromogen  Chemical that absorbs light and produces color. Chromogens are used in laboratory analysis by spectrophotometry.

chromophore  The portion of a molecule that absorbs incident light and emits colored light, usually as a result of the presence of 10 or more double bands or aromatic rings. Chromophores are the colored portions of chromogens and are synthesized in molecules to provide measurable color in laboratory assays.

chromosome  Threadlike nuclear structure composed of condensed DNA that transmits genetic information. In humans there are 46 chromosomes, including 22 homologous pairs of autosomes and 1 pair of sex chromosomes, X and Y.

chronic  Persisting over a long period of time, often for the remainder of a person’s life.

chronic leukemia  Malignant, unregulated proliferation of myelocytic or lymphocytic cells that appear at several stages of differentiation in peripheral blood. Characterized by slow onset and progression of symptoms.

Clinical and Laboratory Standards Institute (CLSI)  Global nonprofit agency that uses consensus to develop and publish healthcare guidelines and standards.

Clinical Laboratory Improvement Amendments (CLIA) of 1988  Law establishing the Clinical Laboratory Improvement Amendments Committee (CLIAC), which sets and enforces standards for quality testing in the clinical laboratory.

clone  Group of genetically identical cells derived from a single common cell through mitosis.

Clostridium perfringens  Anaerobic gram-positive bacteria that cause gangrene in humans. Symptoms of gangrene include intravascular hemolysis and thrombosis.

cluster of differentiation (CD)  Cell surface membrane receptors or markers used to characterize cells by their functions. CD profiles are used in flow cytometry to identify cell types. CDs are used in hematology to identify cell clones associated with lymphoid and myelogenous leukemias and lymphomas.

coagulation  Series of enzymatic reactions beginning with activation of factor VII by tissue factor (extrinsic/in vivo) or factor XII by a negatively charged surface (intrinsic/in vitro) and proceeding through the common pathway to the formation of an insoluble fibrin clot.

coagulation cascade  Series of enzymatic reactions beginning with activation of factor VII by tissue factor (extrinsic/in vivo) or factor XII by a negatively charged surface (intrinsic/in vitro) and proceeding through the common pathway to the formation of an insoluble fibrin clot.

coagulation factors  Plasma proteins, also called procoagulants, that circulate as inactive forms. When activated in the process of coagulation, procoagulants participate in the coagulation cascade to form a fibrin clot.

codocyte (target cell)  Poorly hemoglobinized red blood cell (RBC) that appears in hemoglobinopathies, thalassemia, and liver disease. In a Wright-stained peripheral blood film, hemoglobin concentrates in the center of the RBC and around the periphery, causing the cell to resemble a “bull’s-eye.”

coefficient of variation (CV, percent CV, CV%)  Statistical measure of the deviation of a variable from its mean divided by the mean, usually expressed as a percentage.

colchicine  Alkaloid that blocks microtubule formation and prevents cell division. Used in cytogenetic studies to arrest mitosis in metaphase so that chromosomes may be karyotyped. Colchicine is also a component of a drug used to treat gout. Colcemid is the trademark for a colchicine derivative used in preparing chromosomes for karyotyping.

cold agglutinin  IgM autoantibody specific for red blood cell surface membrane antigens usually of the Ii system that typically reacts at temperatures below 30° C.

cold agglutinin disease  Acquired autoimmune hemolytic anemia resulting from red blood cell (RBC) agglutination by IgM autoantibodies that react with RBCs at temperatures above 30° C. Patients with cold agglutinin disease experience Raynaud phenomenon, characterized by pallor, cyanosis, and pain in the fingers, palms, wrists, and ankles after exposure to cold.

colony-forming unit (CFU)  Hematopoietic progenitor cells that are derived from the pluripotential hematopoietic stem cell and give rise to the different cell lineages of the bone marrow. Named because of their ability to form colonies in tissue culture.

colony-forming unit–granulocyte, erythrocyte, monocyte, and megakaryocyte (CFU-GEMM)  Hematopoietic progenitor cell capable of differentiating into the granulocytic (myelocytic), erythrocytic (normoblastic), monocytic, or megakaryocytic cell lines.

colony-stimulating factor (CSF)  Cytokine that promotes the division and differentiation of hematopoietic cells.

common coagulation pathway  The steps in the coagulation cascade from the activation of factor X through the conversion of fibrinogen to fibrin. The common pathway begins at the junction of the intrinsic and extrinsic pathways and involves factors X, V, and II (prothrombin) and fibrinogen, in order of reaction.

complement (C)  System of at least 20 serum enzymes. The complement system responds to antigen-antibody reaction to stimulate white blood cell chemotaxis, generate inflammation, and cause red blood cell lysis.

condenser  Substage microscope device that focuses light on the slide-mounted specimen to promote visual clarity.

confidence interval (CI)  Range of values expected to contain the measured value (parameter) with a predetermined degree of statistical confidence. For instance, the 95% confidence interval is expected to include 95% of all values of a parameter measured in a normal population, which corresponds closely to ±2 standard deviations.

congenital  Describes a condition that exists at, and presumably before, birth. Often refers to a hereditary condition.

Coombs test (direct antiglobulin test, DAT)  Screening procedure in which antihuman globulin is used to detect antibodies and complement bound to red blood cells in vivo.

coronary artery bypass grafting (CABG)  Cardiac surgery usually requiring cardiopulmonary bypass and extracorporeal circulation in which occluded sections of coronary arteries are replaced with grafts taken from nearby arteries, for example, the internal mammary artery.

corrected reticulocyte count  Calculation performed to correct the visual reticulocyte count for specimens with a hematocrit below 45% to the equivalent reticulocyte count at a hematocrit of 45%. In anemia, the visual reticulocyte percentage is misleadingly elevated because whole blood contains fewer red blood cells relative to reticulocytes.

Coumadin (warfarin)  Vitamin K antagonist used as an anticoagulant to prevent thrombosis in people with atrial fibrillation, venous thromboembolism, or cardiac insufficiency. Also used prophylactically after orthopedic surgery. Warfarin suppresses vitamin K and reduces the activity of the vitamin K–dependent coagulation factors II (prothrombin), VII, IX, and X.

cryoglobulin  Any of numerous serum globulins, typically immunoglobulins, that precipitate at around 4° C and become resuspended at 37° C.

cryoprecipitate (CRYO)  Therapeutic agent rich in fibrinogen, factor VIII, and factor XIII, used to treat bleeding disorders in fibrinogen deficiency, factor XIII deficiency, and hemorrhagic trauma. Cryoprecipitate is collected from human plasma that has been frozen and slowly thawed.

cyanosis  Bluish discoloration of the skin, sclera, and mucous membranes caused by poor tissue oxygenation. Usually a sign of anemia.

cytochemical analysis  Use of specialized stains to detect cellular enzymes and other chemicals in peripheral blood films and bone marrow aspirate smears. Used to differentiate hematologic diseases, especially leukemias.

cytogenetics  Branch of genetics devoted to the laboratory study of visible chromosome abnormalities, such as deletions, translocations, and aneuploidy.

cytokine  Cellular product that influences the function or activity of other cells. Cytokines include colony-stimulating factors, interferons, interleukins, and lymphokines.

cytomegalovirus (CMV)  Group of DNA viruses of the family Herpesviridae. CMV infection is asymptomatic in adults but can be transmitted to a fetus in utero to cause a potentially fatal infection or reduced intelligence. CMV can be transmitted by blood transfusions and is detected using molecular diagnostic techniques.

cytopenia   Reduced cell count in one or more of any blood cell line—red blood cells, white blood cells, or platelets.

cytosol  Fluid portion of the cytoplasm, less granules and organelles, as separated by ultracentrifugation.

cytotoxic  Describes a compound or agent that destroys or damages cells.

dacryocyte (teardrop cell)  Red blood cell with a single pointed extension, resembling a teardrop. Dacryocytes are often seen in the myeloproliferative neoplasm termed myelofibrosis with myeloid metaplasia.

D-dimer (D:D, D-D)  One of the fibrin degradation products. D-dimer is composed of two fibrin D fragments covalently joined by the enzymatic action of factor XIII. The D-dimer assay is used to rule out venous thromboembolic disease and disseminated intravascular coagulation, and may be used to monitor the efficacy and length of warfarin therapy.

deep vein thrombosis (DVT, deep venous thrombosis)  Pathologic formation of a clot in a deep leg vein such as the femoral vein. A manifestation of venous thromboembolic disease that is associated with a number of acquired or congenital thrombotic risk factors, deep vein thrombosis raises the risk of a pulmonary embolus.

11-dehydrothromboxane B2 (11-DHT)  Measurable urine product of the platelet cyclooxygenase (eicosanoid) activation pathway. Employed clinically to measure in vivo platelet activation and aspirin resistance.

delayed hemolytic transfusion reaction  Hemolysis that occurs days or weeks after a blood transfusion, caused by an anamnestic response to the transfused red blood cells in a patient alloimmunized from a previous pregnancy or transfusion.

δ check  Quality control process in which a current analyte result is compared with the result for the same analyte from the previous specimen from the same patient.

dense granule (dense body, δ-body, δ-granule)  Platelet organelle that contains and secretes the small molecules adenosine diphosphate, adenosine triphosphate, serotonin, calcium (Ca2+), and magnesium (Mg2+). There are two to seven dense granules per platelet, and they are named by their opaque appearance in transmission electron microscopy.

deoxyhemoglobin  Hemoglobin that is not combined with oxygen, formed when oxyhemoglobin releases its oxygen to the tissues.

deoxyribonucleic acid (DNA)  Double-stranded, helical nucleic acid that carries genetic information. DNA is composed of nucleotide sequences with four repeating bases: adenine, cytosine, guanine, and thymine. During mitosis, DNA condenses to form chromosomes.

des-γ-carboxy coagulation factors and coagulation control proteins  Coagulation cascade procoagulants II, VII, IX, and X; and control proteins C, S, and Z that require vitamin K–catalyzed γ-carboxylation of glutamic acid. During anticoagulant therapy with warfarin (Coumadin), which suppresses vitamin K, these des-γ-carboxylated proteins cannot participate in coagulation.

desquamation  Shedding of epithelial elements, chiefly of the skin, in scales or sheets.

Diamond-Blackfan anemia (DBA, congenital pure red cell aplasia)  Rare congenital anemia due to mutations in DNA repair genes, and evident in the first 3 months of life. Anemia is severe and erythropoietin resistant; the reticulocyte count does not rise. Platelet and white blood cell counts are normal.

diapedesis  Outward passage of white blood cells through intact vessel walls.

differential white blood cell count  Review and tabulation of 100 to 200 white blood cells (WBCs) in a stained blood film. The different types of WBCs are counted and reported as absolute counts or percentages of total WBCs. In automated hematology analyzers, the differential WBC count is accomplished by counting thousands of WBCs using various technologies.

dilute Russell viper venom time (DRVVT)  Coagulation test performed like a prothrombin time assay. Russell viper venom activates the common coagulation pathway at the level of factor X. In the DRVVT assay, the reagent is diluted 1:500. DRVVT is prolonged by lupus anticoagulant, and the test is used routinely in screening for this antibody.

diploid  Having two sets of chromosomes, as normally found in nuclei of somatic cells. In humans, the normal diploid number is 46.

direct antiglobulin test (DAT, Coombs test)  Screening procedure in which antihuman globulin is used to detect antibodies and complement bound to red blood cells in vivo.

direct thrombin inhibitors (DTIs)  Class of intravenous therapeutic anticoagulants including argatroban, dabigatran, and bivalirudin that suppress coagulation by directly neutralizing thrombin. DTIs are used in place of heparin when heparin-induced thrombocytopenia with thrombosis is suspected. DTI therapy may be monitored using the partial thromboplastin time.

disseminated intravascular coagulation (DIC)  Uncontrolled activation of thrombin and consumption of coagulation factors, platelets, and fibrinolytic proteins secondary to many initiating events, including infection, inflammation, shock, and trauma. Most commonly evidenced by diffuse mucocutaneous bleeding.

Döhle bodies  In Wright-stained peripheral blood films, gray to light blue round or oval inclusions composed of ribosomal RNA found singly or in multiples near the inner membrane surface of granulocyte cytoplasm.

dominant  Denoting an inherited allele whose trait is expressed whenever the gene is present, even in heterozygotes.

Donath-Landsteiner (D-L) autoantibody  IgG autoantibody with anti-P specificity that binds red blood cells at temperatures below 20° C and causes hemolysis at 37° C. Donath-Landsteiner antibody causes hemolysis in patients with paroxysmal cold hemoglobinuria.

Down syndrome  Congenital group of physical, mental, and functional abnormalities including distinctive facial features, congenital heart disease, muscular hypotonia, and mental retardation, all associated with trisomy 21. Approximately 10% of infants with Down syndrome are born with or develop transient myeloproliferative disease (TMD), which resembles chronic myelogenous leukemia but resolves spontaneously. Within a few weeks of TMD resolution, the child has a 10% to 30% chance of developing acute myeloid or acute lymphoblastic leukemia.

drepanocyte (sickle cell)  Abnormal crescent-shaped red blood cell containing hemoglobin S, characteristic of sickle cell anemia.

drug-induced hemolytic anemia  Hemolytic anemia caused directly by a drug or secondary to an antibody-mediated response stimulated by the drug.

dry tap  Term used when an inadequate sample of bone marrow fluid is obtained during bone marrow aspiration. Dry taps occur when the marrow is packed, as in chronic myelogenous leukemia, or when it is fibrotic, as in myelofibrosis with myeloid metaplasia.

duodenum  Proximal portion of the small intestine adjacent to the stomach.

dyscrasia  Disorder of a hematologic cell line or lines.

dyserythropoiesis  Deranged erythropoiesis producing cells with abnormal morphology; usually applied to congenital dyserythropoietic anemia and myelodysplastic syndrome.

dysfibrinogenemia  Presence in the plasma of structurally abnormal fibrinogen; often a result of liver disease, occasionally congenital.

dysmegakaryopoiesis  Defective megakaryocytic production and maturation characterized by cells with abnormal morphology and increased or decreased megakaryocyte counts.

dysmyelopoiesis  Defective myelocytic production and maturation characterized by cells with abnormal morphology; often applied to myelodysplastic syndromes.

dysplasia  Abnormal growth pattern; for example, enlarged skull in chronic anemia. Abnormal cervical epithelial cell histopathologic features.

dyspnea  Difficult or painful breathing.

ecchymosis  Hemorrhagic spot, 1 cm or larger in diameter, in the skin or mucous membranes, typically forming an irregular blue or purplish patch. Also known as a bruise.

echinocyte (burr cell, crenated red blood cell)  Red blood cell (RBC) with short, equally spaced, spiny projections. Burr cells are found in uremia and pyruvate kinase deficiency, and observed in all fields of a peripheral blood film. Crenated RBCs are formed by cellular dehydration (drying artifact), and not observed in all fields.

eclampsia  Potentially life-threatening disorder during pregnancy characterized by hypertension, generalized edema, proteinuria, and convulsions.

edema  Accumulation of excess serous fluid in a fluid compartment or tissue.

effusion  Seepage and accumulation of plasma-derived fluid into a body cavity from blood vessels as a result of blood vessel damage or hydrostatic pressure.

electronic impedance  Opposition to the flow of electrical current. The impedance principle of cell counting is based on the detection and measurement of changes in electrical resistance produced by cells as they transverse a small aperture in a conducting solution.

electrophoresis  Separation and identification of proteins, nucleic acids, and hemoglobin types based on their relative rates of migration through agarose or polyacrylamide gel in an applied electrical field. Depending on the component, the rate of migration may be based on molecular mass and/or net charge.

elliptocytes (ovalocytes)  Oval red blood cells seen in the peripheral blood in the membrane disorder hereditary elliptocytosis. May be found in low numbers in healthy states and in other anemias such as iron deficiency and thalassemia.

elliptocytosis (ovalocytosis)  Hereditary hematologic disorder characterized by the presence of elliptocytes; often asymptomatic but may be associated with slight anemia.

Embden-Meyerhof pathway (EMP, glycolysis)  A series of enzymatically catalyzed reactions by which glucose and other sugars are metabolized to yield lactic acid (anaerobic glycolysis) or pyruvic acid (aerobic glycolysis). Metabolism releases energy in the form of adenosine triphosphate.

embolism  Pathologic event in which an embolus (foreign object) travels through the bloodstream, becomes lodged in an artery, and obstructs blood flow. The embolus is often a blood clot, but it may be a fat globule, air bubble, piece of tissue, or clump of bacteria. Emboli occlude an artery and cause tissue ischemia, necrosis, and loss of function. A pulmonary embolism is an embolus in a lung artery and is often fatal.

endoplasmic reticulum (ER)  Extensive network of membrane-enclosed tubules in the cytoplasm of cells. Rough endoplasmic reticulum is rich in ribosomes that synthesize proteins and provides a pathway for transport of membrane-bound protein through the cytoplasm.

endothelial cells  Cell layer that lines the inner surface of all blood vessels. Intact endothelial cells prevent thrombosis because they present a smooth, nonactivating surface and secrete antiplatelet and anticoagulant substances. Injured endothelial cells promote clotting through expression of tissue factor and secretion of coagulation-promoting factors, such as von Willebrand factor.

enterocytes  Epithelial cells that form the inner lining of the intestine. Enterocytes absorb nutrients from the intestinal lumen and transport them to the portal circulation.

eosinophil  Granulocyte with large uniform cytoplasmic granules that stain orange to pink with Wright stain. Granules usually do not obscure the segmented nucleus.

eosinophilia  Increase in the blood eosinophil count that is associated with allergies, parasitic infections, or hematologic disorders.

epiphyses  Ends of long bones that normally contain hematopoietic tissue.

epistaxis  Hemorrhage from the nose; a nosebleed that requires intervention.

Epstein-Barr virus (EBV)  Herpesvirus that causes infectious mononucleosis and leads to the appearance of variant lymphocytes.

erythroblastosis fetalis (hemolytic disease of the fetus and newborn, HDFN)  Alloimmune anemia caused by maternal immunoglobulin G antibody that crosses the placenta and binds fetal red blood cell antigens inherited from the father; for instance, maternal anti-A with fetal A antigen. The disorder is characterized by hemolytic anemia, hyperbilirubinemia, and extramedullary erythropoiesis.

erythrocyte (red blood cell, RBC)  Nonnucleated biconcave disk-shaped peripheral blood cell containing hemoglobin. Its primary function is oxygen transport and delivery to tissues.

erythrocyte sedimentation rate (ESR)  Distance that red blood cells fall in a column of anticoagulated blood in a specified time period. Elevated sedimentation rates are not specific for any disorder but indicate the presence of inflammation.

erythrocytosis  Increase in the red blood cell count in peripheral blood.

erythroleukemia (Di Guglielmo disease, M6)  Acute malignancy characterized by a proliferation of erythroid and myeloid precursors in bone marrow, with erythroblasts with bizarre lobulated nuclei and abnormal myeloblasts in peripheral blood.

erythron  Total mass of red blood cells circulating in the peripheral blood and their bone marrow precursors.

erythropoiesis  Bone marrow process of red blood cell production.

erythropoietin (EPO)  Glycoprotein hormone synthesized primarily in the kidneys and released into the bloodstream in response to hypoxia. The hormone acts to stimulate and regulate the bone marrow production of red blood cells.

essential thrombocythemia  Myeloproliferative neoplasm characterized by marked thrombocytosis and dysfunctional platelets. Patients may experience bleeding or thrombosis.

etiology  Causes or origin of a disease, for instance, genetic factors, infection, toxins, or trauma. Contrast with pathogenesis, which is the physiologic and biochemical mechanisms by which a disease progresses.

euchromatin  Portion of DNA that is active in gene expression and stains lightly with Wright stain.

euglobulin  In the euglobulin lysis assay, the fraction of treated plasma that contains fibrinogen, plasmin, plasminogen, and plasminogen activators, but lacks fibrinolytic inhibitors.

exogenous  Originating from outside the body or produced by external causes; used, for example, to describe a disease caused by a bacterial or viral agent foreign to the body.

exon  Portion of a DNA molecule that becomes translated to form a protein product. Exons and introns are transcribed from DNA to heteronuclear RNA, where the introns are excised to form messenger RNA.

extramedullary hematopoiesis (myeloid metaplasia)  Production of blood cells outside the bone marrow, such as in the spleen, liver, or lymph nodes. Extramedullary hematopoiesis usually occurs in response to bone marrow fibrosis and loss of bone marrow hematopoiesis.

extranodal  Located outside a lymph node.

extravascular hemolysis  Destruction of red blood cells outside of a blood vessel, typically by splenic macrophage phagocytosis. Also called macrophage-mediated hemolysis.

extrinsic coagulation pathway  Primary in vivo coagulation pathway. Exposure of tissue factor activates factor VII. Factor VIIa activates factors IX and X, which triggers the common pathway of coagulation and formation of fibrin.

exudate  Fluid that has effused into a body cavity in association with bacterial or viral infections, malignancy, pulmonary embolism, or systemic lupus erythematosus. An exudate is typically cloudy, because it contains cells and concentrated protein.

factor assay  Clot-based or chromogenic assay for specific coagulation factor activity.

factor V Leiden mutation  Substitution of arginine with glutamine at position 506 in the factor V protein. The resultant factor V resists digestion by activated protein C. The factor V Leiden mutation results in increased thrombin production and is a thrombosis risk factor.

Fanconi anemia  Autosomal recessive or X-linked aplastic anemia manifesting in childhood or early adult life. Characterized by mental retardation, absence of the thumb and radius, small stature, hypogonadism, and patchy brown discoloration of the skin.

favism  Acute hemolytic anemia caused by ingestion of fava beans or inhalation of the pollen of the plant. Usually occurs in individuals with an inherited deficiency of glucose-6-phosphate dehydrogenase in red blood cells.

ferritin  Iron-apoferritin complex, a major form in which iron is stored in the liver.

ferrokinetics  Study of iron metabolism, including the movement of iron among the storage, transport, and functional iron compartments.

fibrin  Fibrillar protein produced by the action of thrombin on fibrinogen in the clotting process. Fibrin is responsible for the semisolid character of a blood clot.

fibrin degradation products (FDPs, fibrin split products, FSPs)  Fibrin fragments X, Y, D, and E and D-dimer produced by the action of fibrin-bound plasmin during fibrinolysis.

fibrinogen  Plasma glycoprotein that is converted to fibrin by thrombin digestion.

fibrinolysis  Continual process of digestion of fibrin by bound plasmin that has been activated by bound plasminogen activator. Fibrinolysis is the normal mechanism for the removal of fibrin clots. Fibrin is digested into fragments X, Y, D, and E and D-dimer.

fibroblast  Connective tissue cell that differentiates into numerous cells, which comprise the fibrous tissue of the body, for instance, tissue in the walls of arteries.

Fitzgerald factor (high-molecular-weight kininogen, HMWK)  Member of the kinin inflammatory system that is digested and activated by kallikrein to form bradykinin. Fitzgerald factor is one of the in vitro contact activators of the coagulation system, which also include prekallikrein and factor XII.

Fletcher factor (prekallikrein, PK, pre-K)  Member of the kinin inflammatory system that forms active kallikrein upon digestion by kininogen. Fletcher factor helps to trigger in vitro coagulation contact activation. Fletcher factor deficiency prolongs the partial thromboplastin time but has no clinical consequence.

flow cytometer  Instrument in which cells suspended in fluid flow one at a time through a focused beam of light. The light is scattered in patterns characteristic of the cells and their components. A sensor detecting the scattered or emitted light measures the size and molecular characteristics of individual cells.

fluorescence in situ hybridization (FISH)  Laboratory technique in which fluorescence-labeled nucleic acid probes hybridize to selected DNA or RNA sequences in fixed tissue. FISH allows for the visual microscopic detection of specific polymorphisms or mutations such as BCR/ABL in cell or tissue specimens.

fluorophore  Portion of a molecule that absorbs incident light and emits fluorescent light. Fluorophores are synthesized in molecules to provide measurable fluorescence in laboratory assays.

free erythrocyte protoporphyrin (FEP)  Porphyrin precursor of heme that is present in low concentrations in normal red blood cells (RBCs). Elevated RBC concentrations indicate iron deficiency or impaired iron insertion.

French-American-British (FAB) classification  International classification system for acute leukemias, myeloproliferative neoplasms, and myelodysplastic syndromes developed in the 1970s and 1980s. Still in use, although it is being displaced by the World Health Organization classification.

fresh frozen plasma (FFP)  Plasma that is separated by centrifugation from whole-blood donations and frozen within 8 hours of collection. FFP contains all of the plasma procoagulants and control proteins, including the labile factors V and VIII. FFP is used for replacement therapy in acquired multiple-factor deficiencies, or in single-factor deficiencies when factor concentrates are not available.

G banding (GTG banding)  In cytogenetic analysis, a procedure in which metaphase chromosomes are treated with trypsin and then stained with Giemsa dye. The areas rich in adenine-thymine, called G+, stain intensely, whereas the areas rich in guanine-cytosine (G–) stain more lightly. The G+ bands correspond with Q bands in Q banding. Banding patterns are used for the identification of chromosomes.

gammopathy  Plasma protein imbalance caused by markedly increased concentrations of gamma globulin. A monoclonal protein produced by myeloma tumor cells causes most gammopathies.

Gaucher disease  Rare autosomal recessive disorder of fat metabolism caused by glucocerebrosidase deficiency and characterized by histiocytic hyperplasia in the liver, spleen, lymph nodes, and bone marrow. The characteristic Gaucher cells, which are lipid-filled macrophages whose cytoplasm resembles crumpled tissue paper, are found on the Wright-stained bone marrow aspirate smear.

Gaussian distribution  Frequency distribution that approximates the distribution of many random variables and is portrayed graphically as a symmetric bell-shaped curve. The peak represents the mean of the distribution and the width of the curve represents the dispersion or variability, which is generally expressed in terms of standard deviation from the mean. Also called a normal distribution.

gene  Segment of a DNA molecule that contains all the information required for synthesis of a protein, including both coding (exon) and noncoding (intron) sequences. Each gene occupies a specific position (locus) on a particular chromosome.

gene rearrangement  Reorganization of the DNA sequences of a gene. Rearrangement of B-cell and T-cell genes produces an infinite variety of variable-region receptor and immunoglobulin sequences. Clonalgene rearrangements occur in lymphoma and lymphocytic leukemia and are detected by flow cytometry to identify these diseases.

gestational age  Age of the fetus, usually expressed as the time elapsed from the first day of the mother’s last menstrual period.

Glanzmann thrombasthenia (GT)  Severe mucocutaneous bleeding disorder caused by one of a series of mutations in platelet glycoprotein (GP) IIb or IIIa. Normal GP IIb/IIIa recognizes and binds the arginine-glycine-aspartate peptide sequence receptor complex found in fibrinogen and von Willebrand factor. Glanzmann thrombasthenia causes a defect of fibrinogen-dependent platelet aggregation.

globin  Protein constituent of hemoglobin. Two identical pairs of globin chains bind four heme molecules to form hemoglobin.

globulins  Class of proteins that are insoluble in water or highly concentrated salt solutions but are soluble in moderately concentrated salt solutions. All plasma proteins are globulins except albumin and prealbumin.

glossitis  Inflammation of the tongue that causes it to be red and smooth.

glucose-6-phosphate dehydrogenase (G6PD)  First enzyme of the glucose monophosphate shunt from the Embden-Meyerhoff pathway. G6PD catalyzes the oxidation of glucose-6-phosphate to a lactone, converting the oxidized form of nicotinamide adenine dinucleotide phosphate (NADP) to the reduced form (NADPH).

glucose-6-phosphate dehydrogenase deficiency  X-linked recessive deficiency of glucose-6-phosphate dehydrogenase characterized by episodes of acute intravascular hemolysis under conditions of oxidative stress, including exposure to oxidative drugs such as quinine.

glycocalyx  Glycoprotein and polysaccharide covering that surrounds many cells. The platelet glycocalyx is thicker than that of other cells and provides a procoagulant environment.

glycolysis (Embden-Meyerhof pathway, EMP)  A series of enzymatically catalyzed reactions by which glucose and other sugars are metabolized to yield lactic acid (anaerobic glycolysis) or pyruvic acid (aerobic glycolysis). Metabolism releases energy in the form of adenosine triphosphate.

glycophorin  Transmembrane red blood cell protein that carries several blood group antigens.

glycoprotein  Conjugated protein containing one or more covalently linked carbohydrate residues.

glycoprotein IIb/IIIa (GP IIb/IIIa)  Pair of glycoproteins that function as a receptor for the arginine-glycine-aspartate sequence in fibrinogen and von Willebrand factor. The combination of fibrinogen and glycoprotein IIb/IIIa is essential to platelet aggregation.

Golgi apparatus  Rigid organelle comprised of numerous flattened sacs and associated vesicles. It is the location of the posttranslational modification and storage of glycoproteins, lipoproteins, membrane-bound proteins, and lysosomal enzymes.

gout  Painful inflammation caused by excessive plasma uric acid, which becomes deposited as monosodium urate monohydrate in joint capsules and adjacent tendons.

graft-versus-host disease (GVHD)  Condition including tissue rejection that occurs when immunologically competent cells or their precursors are transplanted into an immunocompromised host who is not histocompatible with the donor. The donor cells engraft and mount an immune response against the host.

granulocytes  Class of white blood cells in peripheral blood characterized by cytoplasmic granules; includes basophils, eosinophils, and neutrophils.

granuloma  Nodular, delimited aggregation of inflammatory cells, macrophages, and macrophage-derived multinucleate giant cells surrounded by a rim of lymphocytes and fibroblasts. Granulomas are major sites of cell-mediated immune response to particulate antigens, and they may occur in many organs in chronic granulomatous disease.

GTG banding (G banding)  In cytogenetic analysis, a procedure in which metaphase chromosomes are treated with trypsin and then stained with Giemsa dye. The areas rich in adenine-thymine, called G+, stain intensely, whereas the areas rich in guanine-cytosine (G–) stain more lightly. The G+ bands correspond with Q bands in Q banding. Banding patterns are used for the identification of chromosomes.

guaiac test  Test performed on stool emulsions to detect hemoglobin as evidence of gastrointestinal bleeding. Small amounts of blood may be invisible; therefore it is known as a test for occult (hidden) blood. The peroxidase activity of hemoglobin in blood reacts with guaiac to yield a blue color.

hairy cells  Malignant B lymphocytes seen in the peripheral blood and bone marrow characterized by delicate gray cytoplasm with projections resembling hairs. These cells are seen in hairy cell leukemia.

haploid  Referring to the number of chromosomes found in sperm or ova, which is only one of each pair of chromosomes found in somatic (diploid) cells. In humans, the haploid number is 23.

haptoglobin  Plasma protein that irreversibly binds free hemoglobin, forming a complex that is removed by macrophages while conserving iron. Haptoglobin is decreased due to consumption in intravascular hemolysis.

Heinz bodies  Round blue to purple inclusions attached to inner red blood cell membranes visible when stained with new methylene blue dye. Heinz bodies may be found in multiples and are composed of precipitated hemoglobin in unstable hemoglobin disorders and glucose-6-phosphate dehydrogenase deficiency.

helmet cell  Helmet-shaped schistocyte that may appear in microangiopathic hemolytic anemia (fragmented red blood cell).

hemarthroses  Chronic joint bleeds that cause inflammation and immobilization; a symptom of severe hemophilia.

hematemesis  Vomiting of bright red blood.

hematocrit (HCT, packed cell volume, PCV)  Proportion of whole blood that consists of red blood cells, expressed as a percentage of the total blood volume.

hematoidin  Golden yellow, brown, or red crystals that are chemically similar to bilirubin. Hematoidin crystal in a tissue preparation indicates a hemorrhage site.

hematology  Clinical study of blood cells and blood-forming tissues.

hematoma  Localized collection of extravasated blood (blood that has escaped from vessel into tissue), usually clotted, in an organ space or tissue, giving the appearance of a bruise.

hematopathology  Study of the diseases of blood cells and hematopoietic tissue.

hematopoiesis  Formation and development of blood cells. Hematopoiesis occurs mostly in the bone marrow and peripheral lymphatic tissues.

hematopoietic microenvironment  Matrix of bone marrow stromal cells and tissue that supports hematopoiesis both structurally and through the production of cytokines and colony-stimulating factors.

hematopoietic progenitor cell (HPC)  Actively dividing cell that is committed to a single blood cell lineage and is not capable of self-renewal. Therapeutic hematopoietic progenitor cell products intended for transplantation provide both hematopoietic stem cells and progenitor cells.

hematopoietic stem cell (HSC)  Actively dividing cell that is capable of self-renewal and of differentiation into any blood cell lineage.

hematuria  Abnormal presence of intact red blood cells in the urine; indicative of kidney or urinary tract disease.

heme  Pigmented iron-containing nonprotein part of the hemoglobin molecule. There are four heme groups in a hemoglobin molecule, each containing one ferrous ion in the center. Oxygen binds the ferrous ion and is transported from an area of high to low oxygen concentration.

hemochromatosis  Disease of iron metabolism that is characterized by excess deposition of iron in the tissues. The disease may be inherited or may develop as a complication of a hemolytic anemia, such as β-thalassemia major.

hemoconcentration  Elevation of the red blood cell, white blood cell, and platelet counts resulting from a decrease in plasma volume, for example, in dehydration.

hemocytometer (hemacytometer, counting chamber)  Device used to perform visual blood and body fluid cell counts, consisting of a microscopic slide with a depression whose polished glass base is marked with grids and into which a measured volume of a sample of diluted blood is placed and covered with a cover glass. The number of cells in the squares is counted under a microscope and used as a representative sample for calculating the unit volume.

hemodialysis  Extracorporeal circulation process that substitutes for the kidneys and removes wastes from the blood. Hemodialysis is used to treat patients with renal failure. The patient’s blood is shunted from the body through a dialysis machine for diffusion and ultrafiltration and is then returned to the patient’s circulation.

hemoglobin (Hb, HGB)  Tetramer composed of two identical globin chains, each of which binds a heme molecule. Hemoglobin is the primary constituent of red blood cell cytoplasm and transports molecular oxygen from the lungs to the tissues.

hemoglobin C crystal  Reddish hexagonal cytoplasmic red blood cell crystal described as a “gold bar, ” or “Washington monument.” Typical of homozygous hemoglobin C disease, crystals form as deoxyhemoglobin C polymerizes.

hemoglobin electrophoresis  Separation and identification of normal and abnormal hemoglobin types based on their relative rates of migration through agarose or polyacrylamide gel in an applied electric field. The rate of migration depends mainly on net charge. Examples of hemoglobin types include Hb A, Hb C, Hb F, and Hb S.

hemoglobin SC crystal  Irregular reddish cytoplasmic red blood cell crystal described as a “glove” or “pistol.” Typical of compound heterozygous hemoglobin SC disease, the crystals form as deoxyhemoglobin S and C polymerize.

hemoglobinemia  Presence of free hemoglobin in the blood plasma; indicative of intravascular hemolysis.

hemoglobinopathy  Condition characterized by structural variations in globin genes that result in the formation of abnormal globin chains. Examples are sickle cell anemia and hemoglobin C disease.

hemoglobinuria  Visible reddish free hemoglobin in the urine; indicative of intravascular hemolysis.

hemolysis  Disruption of red blood cell membrane integrity that destroys the cell and releases hemoglobin.

hemolytic anemia  Anemia characterized by a shortened red blood cell (RBC) life span and inability of the bone marrow to adequately compensate by increasing RBC synthesis. Hemolytic anemia may be caused by extrinsic or intrinsic disorders.

hemolytic disease of the fetus and newborn (HDFN, erythroblastosis fetalis)  Alloimmune anemia caused by maternal IgG antibody that crosses the placenta and binds fetal red blood cell antigens inherited from the father: for instance, maternal anti-A with fetal A antigen. HDFN is characterized by hemolytic anemia, hyperbilirubinemia, and extramedullary erythropoiesis.

hemolytic uremic syndrome (HUS)  Severe microangiopathic hemolytic anemia that often follows infection of the gastrointestinal tract by Escherichia coli serotype O157:H7, which produces an exotoxin. It is characterized by renal failure, thrombocytopenia, the appearance of schistocytes on the peripheral blood film, and severe mucocutaneous hemorrhage.

hemopexin  Plasma glycoprotein produced in the liver. Hemopexin binds free plasma heme in the absence of haptoglobin.

hemophilia  Group of hereditary anatomic bleeding disorders caused by a deficiency of a single coagulation factor. The two most common forms are hemophilia A and hemophilia B, deficiencies of factors VIII and IX, respectively.

hemophilia A (classic hemophilia)  Sex-linked recessive anatomic bleeding disorder caused by a deficiency of coagulation factor VIII.

hemophilia B (Christmas disease)  Sex-linked recessive anatomic bleeding disorder caused by a deficiency of coagulation factor IX.

hemophilia C (Rosenthal syndrome)  Autosomal anatomic bleeding disorder caused by a deficiency of coagulation factor XI.

hemorrhage  Acute severe blood loss requiring intervention and transfusions.

hemorrhagic disease of the newborn  Neonatal anatomic bleeding caused by vitamin K deficiency.

hemosiderin  Intracellular storage form of iron found predominantly in liver, spleen, and bone marrow cells. Hemosiderin is a breakdown product of ferritin that appears in iron overload and hemochromatosis. Hemosiderin may be detected microscopically using the Prussian blue iron stain.

hemosiderinuria  Presence in the urine of hemosiderin, which can be visualized using Prussian blue iron stain; most often an indicator of chronic intravascular hemolysis.

hemosiderosis  Increased tissue iron stores without associated tissue damage; may progress to hemochromatosis.

hemostasis  Process by which a series of platelet, endothelial cell, and plasma enzyme systems prevent blood loss through clot formation and maintain blood vessel patency.

heparin  Naturally occurring mucopolysaccharide anticoagulant classified as a glycosaminoglycan. Heparin is produced by basophils and mast cells. Heparin extracted from porcine mucosa is used as a therapeutic anticoagulant.

heparin-induced thrombocytopenia with thrombosis (HIT)  Morbid, often fatal effect of unfractionated heparin therapy. Up to 5% of patients receiving unfractionated heparin therapy for more than 5 days develop an antibody to the heparin-platelet factor 4 complex. The antibody and target antigen complex bind platelet Fc receptors and activate platelets, which causes a decrease in platelet count by greater than 30% and venous and arterial thrombosis.

hepatitis  Inflammation of the liver that damages hepatocytes and releases bilirubin into the plasma.

hepatitis B virus (HBV)  Causative agent of hepatitis B. The virus is transmitted by contaminated blood or blood products, by sexual contact with an infected person, or by the use of contaminated needles and instruments. Severe infection may cause prolonged illness, destruction of liver cells, cirrhosis, increased risk of liver cancer, or death.

hepatocyte  Parenchymal liver cell.

hepatomegaly  Abnormal enlargement of the liver; usually a sign of disease.

hepatosplenomegaly  Abnormal enlargement of the spleen and liver.

hereditary elliptocytosis (ovalocytosis)  Hereditary spectrin defect characterized by the presence of elliptocytes in the peripheral blood; often asymptomatic but may be associated with slight anemia.

hereditary pyropoikilocytosis  Rare hereditary defect of spectrin that causes severe hemolytic anemia beginning in childhood and extreme poikilocytosis with red blood cell morphology resembling that seen in burn patients.

hereditary spherocytosis  Hereditary defect in a cytoskeletal or transmembrane protein that results in loss of red blood cell membrane and causes hemolytic anemia characterized by numerous spherocytes on the peripheral blood film.

hereditary stomatocytosis  Hereditary defect of the red blood cell membrane resulting in a complex group of diseases in which the hemolysis is mild to severe and stomatocytes are seen on the peripheral blood film.

hereditary xerocytosis  Hereditary defect of the red blood cell membrane that results in hemolytic anemia with dehydrated red blood cells and the presence of stomatocytes, target cells, and macrocytes on the peripheral blood film.

heterochromatin  Portion of DNA that is inactive during transcription to messenger RNA and stains deeply with Wright stain.

heterophile antibody  Antibody that reacts with an antigen from a species other than that of the antigen that stimulated its production. For example, patients with infectious mononucleosis caused by the Epstein-Barr virus produce an antibody to the virus but also produce heterophile antibodies that react with sheep or horse red blood cells.

heterozygous  Having two different alleles at corresponding loci on homologous chromosomes. An individual who is heterozygous for a trait has inherited an allele for that trait from one parent and an alternative allele from the other parent. A person who is heterozygous for a genetic disease will manifest the disorder if it is caused by a dominant allele but will remain asymptomatic if the disease is caused by a recessive allele.

high-molecular-weight kininogen (HMWK, Fitzgerald factor)  Member of the kinin inflammatory system that is digested and activated by kallikrein to form bradykinin. HMWK is one of the in vitro contact activators of the coagulation system, which also include prekallikrein and factor XII.

histiocyte (macrophage)  Mononuclear phagocyte found in all tissues; part of the immune system.

histochemical analysis  Use of specialized stains to detect enzymes and other chemicals in tissues.

histocompatibility  Quality or state of immunologic similarity that allows cells or tissues from one individual to be successfully transplanted into another individual. The degree of compatibility is controlled by white blood cell (WBC) surface markers of the human leukocyte antigen (HLA) system of the major histocompatibility complex. Grafts from donors of the immediate family are more compatible than those from unrelated donors.

histogram  Graph of a frequency distribution. In hematology, a histogram is customarily a line graph generated by an automated analyzer that depicts the frequencies of platelet, white blood cell, or red blood cell volumes in a cell population.

histology  Science concerned with the microscopic identification of cells and tissues used to identify cellular and tissue disease.

histone  Nuclear protein that complexes with DNA to form chromatin. Histones provide for DNA folding and condensation and help regulate replication and transcription.

Hodgkin lymphoma  Solid tumor characterized by painless, progressive hypertrophy of lymphoid tissue, first evident in cervical lymph nodes. Characterized by Reed-Sternberg cells and reactive white blood cells in lymphoid tissue and splenomegaly.

homocysteine  Naturally occurring sulfur-containing amino acid formed in the metabolism of dietary methionine. Homocysteine concentration in plasma depends upon adequate intake of protein, vitamin B6, vitamin B12, and folate.

homocysteinemia  Elevated plasma homocysteine, an independent risk factor for arterial thrombosis, typically caused by vitamin B6, vitamin B12, or folate deficiency.

homocysteinuria  Increase or accumulation of homocysteine in urine; indicates an inherited error in an enzyme of the methionine-homocysteine metabolic pathway.

homozygous  Having two identical alleles at corresponding loci on homologous chromosomes. An individual who is homozygous for a trait has inherited one identical allele for that trait from each parent. A person who is homozygous for a genetic disease caused by a pair of recessive alleles manifests the disorder.

Howell-Jolly (H-J) bodies  Round blue to purple inclusions in red blood cells (RBCs), usually one per RBC, visible on Wright-stained peripheral blood films. Howell-Jolly bodies are composed of DNA and may indicate severe anemia or splenectomy.

human leukocyte antigens (HLA, major histocompatibility complex, MHC)  Cell membrane glycoprotein system that forms the basis for antigen presentation in cellular and humoral immunity and enables the immune system to distinguish between self and nonself. HLA class I molecules (HLA-A, -B, -C) are found on most nucleated cells and on platelets. Class II antigens (HLA-DP, -DQ, -DR) are expressed on B lymphocytes, monocytes, macrophages, and dendritic cells.

humoral immunity  Immune response mediated by B lymphocytes, which produce circulating antibodies (immunoglobulins) in reaction to infectious organisms and other foreign antigens.

hybridization  In molecular biology, formation of a partially or wholly complementary nucleic acid duplex by association of single strands; used to detect and isolate specific nucleic acid sequences.

hydrops fetalis  Gross edema of the entire body of a fetus or newborn infant, associated with severe anemia and occurring in hemolytic disease of the fetus and newborn.

hyperbilirubinemia (icterus, bilirubinemia)  Excess bilirubin in the plasma, which imparts a gold color to the plasma; may indicate hemolytic anemia, liver disease, or bile duct occlusion.

hypercellular bone marrow  Bone marrow showing an abnormal increase in the concentration of nucleated hematopoietic cells; potentially associated with leukemia or hemolytic anemia.

hypercoagulability (thrombophilia)  Abnormally increased tendency to develop pathologic thromboses (clots) caused by a number of acquired and congenital factors.

hyperplasia  Abnormally increased number of cells per unit volume of tissue caused by increased cellular division or abnormal retention. In bone marrow, hyperplasia is evident in hypercellularity. Such hyperplasia may cause enlarged joints or an enlarged forehead, called frontal bossing.

hypersegmented neutrophil  Neutrophil with six or more nuclear lobes or segments; often associated with megaloblastic anemia.

hypersplenism  Increased hemolytic activity of the spleen caused by splenomegaly, resulting in deficiency of peripheral blood cells and compensatory hypercellularity of the bone marrow.

hypertension  Persistently elevated blood pressure.

hyperuricemia  Excess of plasma uric acid or urates; sometimes associated with gout.

hypocellular bone marrow  Abnormal decrease in the number of nucleated hematopoietic cells present in the bone marrow; may be associated with aplastic anemia or fibrosis.

hypochromia  Abnormal decrease in the hemoglobin content of red blood cells so that they appear pale with a larger central pallor when stained with Wright stain. These cells are called hypochromic.

hypodiploid  Having fewer than the normal number of somatic cell chromosomes; for example, fewer than 46 chromosomes in humans.

hypoplasia  Underdevelopment of an organ or tissue, usually resulting from a fewer-than-normal number of cells. A hypoplastic bone marrow is one in which the distribution of nucleated hematopoietic cells is reduced, as in aplastic anemia or fibrosis.

hypoxia  Diminished availability of oxygen to body tissues, usually secondary to decreased lung capacity or decreased oxygen-carrying capacity of the blood.

icterus (bilirubinemia, hyperbilirubinemia)  Excess bilirubin in plasma, which imparts a gold color to the plasma; may indicate hemolytic anemia, liver disease, or bile duct occlusion.

idiopathic  Without a known cause.

immediate transfusion reaction  Hemolysis that begins within minutes or hours of a blood transfusion and is most commonly caused by an incompatibility of the ABO system.

immersion oil  Optically clear oil placed in the space between a microscopic specimen and the microscope objective lens. Oil raises the refractive index, improving resolution.

immune hemolytic anemia  Anemia resulting from shortened red blood cell (RBC) life span caused by antibodies to RBC membrane antigens or complement. The immunoglobulin- or complement-coated RBCs are cleared by splenic macrophages. Anemia results when the bone marrow fails to compensate for RBC consumption.

immune thrombocytopenic purpura (ITP, idiopathic thrombocytopenic purpura, autoimmune thrombocytopenic purpura, AITP)  Mucocutaneous bleeding secondary to thrombocytopenia caused by a platelet-specific autoantibody that shortens platelet life span. Acute ITP occurs more often in children, while chronic ITP occurs more often in middle-aged adults, more commonly in women than in men.

immunoblast  Large mitotically active T or B lymphocyte formed as a result of antigenic stimulation.

immunocompromised  Unable to mount an adequate immune response due to disease or treatment with an immunosuppressive agent. An immunocompromised patient is susceptible to bacterial and viral infections.

immunocytochemical assays  Laboratory tests in which antibodies labeled with chromophores or fluorophores hybridize specific cellular proteins or nucleic acids to produce a measurable color or fluorescent reaction.

immunoglobulin (antibody)  Protein of the γ-globulin fraction produced by B lymphocytes and plasma cells that recognizes and binds a specific antigen. Immunoglobulins are the basis of humoral immunity.

immunophenotyping  Classification of white blood cells and platelets by their membrane antigens. Synthetic antibodies, often monoclonal antibodies produced by hybridoma technology, are used to identify the antigens in flow cytometry.

immunosuppression  Abnormal state of the immune system characterized by its inability to respond to antigenic stimuli. Immunosuppressive drugs are used to reduce immune responses, particularly in tissue transplant therapy.

infectious mononucleosis  Acute infection caused by the Epstein-Barr virus, a herpesvirus. Characterized by fever, sore throat, lymphadenopathy, variant lymphocytes, splenomegaly, hepatomegaly, abnormal liver function, and bruising. Laboratory tests used to identify the disease include blood film review for variant lymphocytes, serologic mononucleosis testing, and molecular identification of Epstein-Barr virus.

integrin  Any of a family of cell-adhesion receptors that mediate interactions between cells and between cells and the extracellular matrix.

interferon  Natural glycoprotein produced by lymphocytes exposed to a virus or another foreign particle of nucleic acid. Interferon induces the production of translation inhibitory protein (TIP) in noninfected cells. TIP blocks the translation of viral RNA and thus gives other cells protection against the original as well as other viruses.

interleukin (IL)  Any of a group of compounds that are synthesized by lymphocytes, macrophages, and matrix cells in the marrow and interact with cells to initiate, stimulate, or influence the maturation of blood cells.

international normalized ratio (INR)  Index computed to normalize prothrombin time (PT) results worldwide. The activity of a PT reagent (thromboplastin) is characterized by manufacturers using the international sensitivity index (ISI), which compares the reagent to the international reference thromboplastin preparation provided by the World Health Organization. Local PTs are adjusted using the following formula: INR = (PTpatient/PTnormal)ISI, where PTpatient is the individual patient’s PT and PTnormal is the geometric mean of the PT reference interval.

international reference preparation (IRP)  Human brain–derived thromboplastin maintained by the World Health Organization. Thromboplastin manufacturers worldwide compare their reagents’ sensitivity with that of this reference preparation using orthogonal regression to generate an international sensitivity index (ISI) for their products.

international sensitivity index (ISI)  Index comparing the sensitivity of a given thromboplastin preparation with the sensitivity of the international reference preparation as determined using orthogonal regression. The international sensitivity index is used as an exponent in the equation for calculating the international normalized ratio.

intracranial hemorrhage (ICH, hemorrhagic stroke)  Bleeding into the brain causing tissue death. Fifteen percent of strokes are caused by intracranial hemorrhage; the remainder are caused by vascular occlusion (ischemia).

intramedullary hematopoiesis  Formation and development of blood cells within the marrow cavity of a bone.

intramuscular (IM)  Injected into muscle tissue.

intravascular hemolysis  Red blood cell destruction that occurs within the blood vessels at a rate exceeding splenic macrophage clearance capacity, releasing hemoglobin into the plasma. Seen in acute hemolytic episodes such as those associated with transfusion reaction, glucose-6-phosphate dehydrogenase deficiency, and sickle cell anemia crisis.

intrinsic coagulation pathway  Sequence of serine protease reactions leading to fibrin formation, beginning with the in vitro contact activation of factor XII, followed by the sequential activation of factors XI and IX, and resulting in the activation of factor X, which initiates the common pathway of coagulation.

intrinsic factor (IF)  Glycoprotein secreted by parietal cells of the gastric mucosa that is essential for the intestinal absorption of vitamin B12. A deficiency of, or antibody to, intrinsic factor results in B12 deficiency.

intron  Nontranslated sequence in a gene. Introns are transcribed to heteronuclear RNA and are excised during the subsequent formation of messenger RNA.

inversion  Structural chromosome alteration caused by breaks at two locations, reversal of direction of the detached sequence, and reattachment. Inversions have little effect on somatic DNA but cause loss of DNA information in offspring.

iron deficiency anemia  Microcytic, hypochromic anemia caused by inadequate supplies of the iron needed to synthesize hemoglobin and characterized by pallor, fatigue, and weakness. Often caused by low dietary iron intake or chronic blood loss.

isoantibody (alloantibody)  Antibody that is produced in response to the presence of foreign antigens; for instance, an antibody to a therapeutic coagulation factor that may render factor therapy ineffective.

jaundice  Orange-yellow discoloration of the skin, mucous membranes, and sclera. Caused by elevated plasma bilirubin, which signals hepatitis, hemolytic anemia, or common bile duct obstruction.

karyorrhexis  Nuclear necrosis in which the nucleus ruptures and chromatin disintegrates into formless granules.

karyotype  Number, form, size, and arrangement of the chromosomes within the nucleus. In cytogenetic laboratory assays mitosis is halted in metaphase and the chromosomes are recorded in a photomicrograph to generate the karyotype.

kinin  Any of a group of polypeptides that trigger inflammatory activity such as contraction of smooth muscle, vascular permeability, and vasodilation. Examples of kinins are bradykinin and kallidin.

kininogen  Either of two plasma α2-globulins that are kinin precursors, called high-molecular-weight kininogen and low-molecular-weight kininogen.

Kleihauer-Betke stain (acid elution slide test)  Test for detecting fetal red blood cells (RBCs) in the maternal circulation. Blood films are immersed in an acid buffer, which causes adult hemoglobin (Hb A) to be eluted from RBCs. The film is stained, and RBCs that have fetal hemoglobin (Hb F) take up the stain.

Köhler illumination  Light microscope illumination system that consists of a substage light source, field diaphragm, condenser, and aperture diaphragm. These are adjusted in sequence to optimize specimen illumination, resolution, contrast, and depth of field.

koilonychia  Dystrophy of the fingernails in which they become thin, ridged, and concave. Associated with iron deficiency anemia.

Kupffer cells  Fixed, highly phagocytic macrophages that line the liver sinusoids. Kupffer cells function like splenic macrophages (littoral cells) to clear senescent red blood cells, immune complexes, and foreign materials.

lactate dehydrogenase (LD)  Enzyme that catalyzes the reversible conversion of lactate to pyruvate. It is widespread in tissues and is particularly abundant in the kidneys, skeletal muscle, liver, red blood cells, and myocardium. The lactate dehydrogenase assay may be used to detect and monitor cell necrosis in these organs, for instance, acute myocardial infarction or as an indicator of intravascular hemolysis.

Langerhans  cell Immature dendritic macrophage (histiocyte) with an irregular nucleus and distinctive racquet-shaped cytoplasmic granules called Birbeck bodies normally found in the epidermis, oral and vaginal mucosa, and lungs. Langerhans cells have been identified as the cells of origin for a nonproliferating epidermal neoplasm known as Langerhans cell histiocytosis.

leptocyte  Abnormal mature red blood cell that is thin and flat with hemoglobin at the periphery and increased central pallor.

leukemia  Group of malignant neoplasms of hematopoietic tissues characterized by diffuse replacement of bone marrow or lymph nodes with abnormal proliferating white blood cells and the presence of leukemic cells in the peripheral blood. Leukemia may be chronic or acute and myeloid or lymphoid.

leukemoid reaction (LR)  Clinical syndrome resembling leukemia in which the white blood cell count is elevated to greater than 50, 000/μL in response to an allergen, inflammatory disease, infection, poison, hemorrhage, burn, or severe physical stress. Leukemoid reaction usually involves granulocytes and is distinguished from chronic myelogenous leukemia by the use of the leukocyte alkaline phosphatase staining of neutrophils.

leukocyte  One of the formed elements of the blood. The five families of WBCs are lymphocytes, monocytes, neutrophils, basophils, and eosinophils. WBCs function as phagocytes of bacteria, fungi, and viruses; detoxifiers of toxic proteins that may be produced by allergic reactions and cellular injury; and immune system cells.

leukocytosis  Abnormally elevated white blood cell count in peripheral blood.

leukoerythroblastic  Characterized by the presence of immature red blood cells and granulocytes in the peripheral blood and bone marrow.

leukopenia  Abnormal decrease in the white blood cell count in peripheral blood.

leukopoiesis  Process by which white blood cells form and develop in the bone marrow and lymph nodes.

Levey-Jennings chart  Quality control chart used to plot periodic test results for control specimens. The chart indicates the mean and the 1, 2, and 3 standard deviation intervals on both sides of the mean. Deviation from this standard distribution indicates the occurrence of a systematic analytical error.

ligand  Molecule, ion, or group bound to the central atom of a chemical compound; for example, the oxygen molecule in hemoglobin, which is bound to the central iron atom. Also, a molecule that binds to another molecule; used especially to refer to a small molecule that specifically binds to a larger molecule.

littoral cells  Fixed, highly phagocytic macrophages that line the sinusoid of the spleen. Littoral cells clear senescent red blood cells, immune complexes, and foreign materials.

low-molecular-weight heparin (LMWH)  Heparin with an average molecular weight of 5000 to 8000 Daltons produced by enzymatic or chemical digestion of unfractionated heparin. LMWH is used for prophylaxis, and treatment monitoring is required only in conditions of fluid imbalance, such as obesity, renal disease, and pregnancy. LMWH therapy is monitored using the chromogenic anti–factor Xa heparin assay.

lupus anticoagulant (LA, LAC)  Autoantibody to phospholipid-binding proteins such as β2-glycoprotein I, annexin, and prothrombin. May be present as a primary condition or secondary to a collagen disorder such as systemic lupus erythematosus, Sjögren syndrome, or rheumatoid arthritis. Chronic lupus anticoagulant is associated with venous and arterial thrombosis and spontaneous abortion.

lymphadenopathy  Any disorder characterized by a localized or generalized enlargement of the lymph nodes or lymph vessels.

lymphoblast  Immature cell found in the bone marrow and lymph nodes, but not normally in the peripheral blood; the most primitive, morphologically recognizable precursor in the lymphocytic series, which develops into the prolymphocyte.

lymphocytes  Mononuclear, nonphagocytic white blood cells found in the blood, lymph, and lymphoid tissues. Lymphocytes are categorized as B and T lymphocytes and natural killer cells. They are responsible for humoral and cellular immunity and tumor surveillance.

lymphocytopenia (lymphopenia)  Abnormally reduced lymphocyte count in peripheral blood.

lymphocytosis  Abnormally increased lymphocyte count in peripheral blood.

lymphoid  Resembling or pertaining to lymph or tissue and cells of the lymphoid system.

lymphokines  Biologic response mediators released by both B and T lymphocytes.

lymphoma  Solid tumor neoplasm of lymphoid tissue categorized as Hodgkin or non-Hodgkin lymphoma and defined by lymphocyte morphology and the histologic features of the lymph nodes.

lymphopoiesis  Formation and production of lymphocytes, predominantly in the lymph nodes.

lymphoproliferative  Pertaining to the proliferation of lymphoid cells resulting in abnormally increased lymphocyte counts in peripheral blood, indicating a reactive or neoplastic condition.

lysosomes  Membrane-bound sacs of varying size distributed randomly in the cytoplasm of granulocytes and platelets. Lysosomes contain hydrolytic enzymes that kill ingested bacteria and digest bacteria and other foreign materials.

macrocyte  Red blood cell with an abnormally large diameter seen on a peripheral blood film and an elevated mean cell volume. Associated with folate and vitamin B12 deficiency, bone marrow failure, myelodysplastic syndrome, and chronic liver disease.

macroglobulin  High-molecular-weight plasma globulin, such as α2-macroglobulin or an immunoglobulin of the M isotype. Abnormal monoclonal IgM proteins seen in Waldenström macroglobulinemia.

macrophage (histiocyte)  Mononuclear phagocyte found in all tissues; part of the immune system.

major histocompatibility complex (MHC, human leukocyte antigen, HLA)  Cell membrane glycoprotein system that forms the basis for antigen presentation in cellular and humoral immunity and enables the immune system to distinguish between self and nonself. MHC class I molecules (HLA-A, -B, -C) are found on most nucleated cells and on platelets. Class II antigens (HLA-DP, -DQ, -DR) are expressed on B lymphocytes, monocytes, macrophages, and dendritic cells.

malaise  Vague feeling of discomfort and fatigue, often associated with cancer or anemia.

malaria  Infectious disease caused by one or more of five species of the protozoan genus Plasmodium. Malaria is transmitted from human to human by a bite from an infected Anopheles mosquito.

malignant  Describes a cancerous disease that threatens life through its ability to metastasize.

marker chromosome  In cytogenetic analysis, a chromosome of abnormal size or shape that is an early indicator of neoplastic disease, for instance, the Philadelphia chromosome in chronic myelogenous leukemia.

mast cell  Connective tissue cell that has large basophilic granules containing heparin, serotonin, bradykinin, and histamine. These substances are released from the mast cell in response to immunoglobulin E stimulation.

May-Hegglin anomaly  Rare autosomal dominant disorder characterized by thrombocytopenia and granulocytes that contain cytoplasmic inclusions similar to Döhle bodies.

mean Value that is derived by dividing the total of a set of values by the number of items in the set; the arithmetic average.

mean cell hemoglobin (MCH)  Average red blood cell (RBC) hemoglobin mass in picograms computed from the RBC count and hemoglobin level.

mean cell hemoglobin concentration (MCHC)  Average relative hemoglobin concentration per red blood cell (RBC), expressed in g/dL, computed from the hemoglobin and hematocrit. Relates to Wright-stained RBC color intensity.

mean cell volume (MCV)  Average red blood cell (RBC) volume in femtoliters computed from the RBC count and hematocrit or directly measured by an automated hematology analyzer. Relates to Wright-stained RBC diameter.

megakaryoblast  Least differentiated visually identifiable megakaryocyte precursor in a Wright-stained bone marrow aspirate smear. The megakaryoblast cannot be distinguished visually from the myeloblast but is identified using special immunochemical markers.

megakaryocyte  Largest cell in the bone marrow, measuring 30 to 50 µm and having a multilobed nucleus. Its cytoplasm is composed of platelets, which are released to the blood through the extension of proplatelet processes. Megakaryocytes are identified and enumerated microscopically at low (10×) power on a bone marrow aspirate smear.

megakaryopoiesis (megakaryocytopoiesis)  Production and development of megakaryocytes, the precursors to platelets, in the bone marrow.

megaloblast  Abnormally large, nucleated, immature precursor of the erythrocytic series; an abnormal counterpart to the pronormoblast. Not only does it have a larger diameter, but the nucleus appears more immature than the cytoplasm. Megaloblasts give rise to macrocytic red blood cells and are associated with megaloblastic anemia, usually caused by folate or vitamin B12 deficiency.

menorrhagia  Abnormally heavy or prolonged menstrual periods.

metacentric  Describes a mitotic chromosome having the centromere at the center, with one arm equal in length to the other.

metamyelocyte  Stage in the development of the granulocyte series, located between the myelocyte stage and the band stage. Characterized by mature, granulated cytoplasm and a bean-shaped nucleus.

metaphase  Second phase of mitosis in which the chromosomes are aligned at the equatorial plate. Chromosomes at metaphase are maximally contracted and are most easily identified in cytogenetic analysis.

metaplasia  Conversion of normal tissue cells into another, less differentiated cell type in response to chronic stress or injury. For instance, myeloid metaplasia describes hematopoiesis in the spleen or liver.

metarubricyte (orthochromic normoblast)  Fourth stage of bone marrow erythropoiesis and the last in which the cell retains a nucleus. The nucleus is fully condensed with no parachromatin, and the cytoplasm is 85% hemoglobinized and bluish-pink. When an orthochromic normoblast appears in the peripheral blood, it is called a nucleated red blood cell.

metastasis  Extension or spread of tumor cells to distant parts of the body, usually through the lymphatics or blood vessels.

methemoglobin  Abnormal form of hemoglobin in which the ferrous ion has become oxidized to the ferric state. Methemoglobin cannot carry oxygen.

microangiopathic hemolytic anemia (MAHA)  Condition in which narrowing or obstruction of small blood vessels by fibrin or platelet aggregates results in distortion and fragmentation of red blood cells, hemolysis, and anemia. This causes the appearance of schistocytes on a Wright-stained blood film.

microcyte  Small red blood cell (RBC) with reduced mean cell volume and reduced diameter on Wright-stained peripheral blood film. Microcytes are often associated with iron deficiency anemia and thalassemia.

microfilament  Intracellular protein that supports the cytoskeleton and assists with cell motility.

microtubules  Tubulin protein channels that maintain cellular shape, contribute to motility, and make up mitotic spindle fibers and centrioles.

mitochondria  Round or oval structures distributed randomly in the cytoplasm of a cell. Mitochondria provide the cell’s aerobic energy system by producing adenosine triphosphate.

mitosis  Ordinary process of somatic cell division resulting in the production of two daughter cells that have identical diploid complements of chromosomes.

monoblast  Most undifferentiated morphologically identifiable precursor of the bone marrow monocytic series; develops into the promonocyte.

monoclonal  Pertaining to or designating a group of identical cells or organisms derived from a single cell or organism. Also used to describe products from a clone of cells, such as monoclonal antibodies.

monocyte  Mononuclear phagocytic white blood cell having a round to horseshoe-shaped nucleus with abundant gray-blue cytoplasm filled with fine reddish granules. Circulating precursor to the macrophage, the primary phagocytic cell of most tissues.

monocytopenia  Abnormally low monocyte count in peripheral blood.

monocytosis  Abnormally elevated monocyte count in peripheral blood; may indicate infection or a neoplasm.

mononuclear  Having only one nucleus. Used to describe cells such as monocytes or lymphocytes as distinct from neutrophils, which have nuclei that appear to be multiple and hence are called segmented or polymorphonuclear.

Mott cell  Plasma cell containing colorless cytoplasmic inclusions of immunoglobulin called Russell bodies that appear similar to vacuoles.

multiple myeloma (now called plasma cell myeloma)  Malignant neoplasm in which plasma cells proliferate in the bone marrow, destroying bone and resulting in pain, fractures, and excess production of a monoclonal plasma immunoglobulin.

mutation  Permanent transmissible change in the DNA sequence of a single gene; includes substitution, loss, or gain of one or more nucleotides. Mutations cause the production of abnormal proteins or the loss of a protein.

myelo-  Prefix relating to the bone marrow or spinal cord and used to identify granulocytic precursors of neutrophils.

myeloblast  Least differentiated morphologically identifiable bone marrow precursor of the granulocytic series; develops into the promyelocyte. The appearance of myeloblasts in peripheral blood signals acute leukemia.

myelocyte  Third stage of bone marrow granulocytic series differentiation, intermediate in development between a promyelocyte and a metamyelocyte. In this stage, differentiation of cytoplasmic granules has begun, so myelocytes may be basophilic, eosinophilic, or neutrophilic.

myelodysplastic syndromes (MDSs)  Group of acquired clonal hematologic disorders characterized by progressive peripheral blood cytopenias that reflect defects in erythroid, myeloid, or megakaryocytic maturation.

myelofibrosis  Replacement of bone marrow with fibrous connective tissue.

myeloid  General term used to denote granulocytic cells and their precursors, including basophils, eosinophils, and neutrophils. Lymphoid and erythroid cell lines are excluded, and most morphologists also exclude the monocytic and megakaryocytic cell lines.

myeloid-to-erythroid (M:E) ratio  Proportion of myeloid cells to nucleated erythroid precursors in bone marrow aspirate. The myeloid-to-erythroid ratio is used to evaluate hematologic cell production. Excluded from the myeloid cell count are monocytic and lymphoid precursors and plasma cells.

myelokathexis  Inherited severe neutropenia and lymphopenia characterized by hypersegmented neutrophils and myeloid hyperplasia. Part of WHIM syndrome (warts, hypogammaglobulinemia, infections, and myelokathexis).

myeloperoxidase (MPO)  Enzyme that occurs in primary granules of promyelocytes, myelocytes, and neutrophils and exhibits bactericidal, fungicidal, and virucidal properties. Cytochemical stains that detect myeloperoxidase are used to identify myeloid precursors in acute leukemia.

myeloproliferative neoplasms (MPN, myeloproliferative disorders, MPD)  Group of neoplasms characterized by proliferation of myeloid tissue and elevations in one or more myeloid cell types in the peripheral blood. Myeloproliferative neoplasms include myelofibrosis with myeloid metaplasia, essential thrombocythemia, polycythemia vera, and chronic myelogenous leukemia.

myoglobin  Monomeric heme-containing protein in muscle. Combines with oxygen released by red blood cells, stores it, and transports it to the mitochondria of muscle cells, where it generates energy.

necrosis  Localized tissue death that occurs in groups of cells in response to disease or injury.

neonatal  Pertaining to the first 28 days after birth.

neoplasm  Any abnormal growth of new tissue; can be malignant or benign. The term is usually applied to cancerous cells.

neuropathy  Any disorder affecting the nervous system.

neutropenia  Abnormally reduced neutrophil count in peripheral blood. Often associated with chemotherapy, it exposes the patient to the risk of infection.

neutrophil  Mature segmented (polymorphonuclear) white blood cell with fine pink-staining cytoplasmic granules in a Wright-stained peripheral blood film. Neutrophils ingest bacteria and cellular debris.

neutrophilia  Abnormally elevated neutrophil count in peripheral blood; often indicates bacterial infection and may be associated with chronic myelogenous leukemia.

nondisjunction  Faulty distribution of chromosomal elements during mitosis or meiosis.

non-Hodgkin lymphoma (NHL)  Solid tumors of lymphoid tissue classified by histologic features and lymphocytic morphology. Should be distinguished from Hodgkin lymphoma, which is caused by proliferation of Reed-Sternberg cells and accumulation of reactive peripheral blood cells.

nonsteroidal antiinflammatory drugs (NSAIDs)  Antiinflammatory, analgesic, and antiplatelet drugs, other than steroids. NSAIDs include aspirin, which acetylates cyclooxygenase and reduces platelet activation, as well as naproxen, acetaminophen, and ibuprofen.

normochromic  Describes a Wright-stained red blood cell with normal color and normal hemoglobin content with a mean cell hemoglobin concentration within the reference interval.

normocyte  Normal, mature red blood cell with a mean cell volume within the reference interval.

nucleated red blood cell (NRBC)  Red blood cell (RBC) in peripheral blood that possesses a nucleus; often an orthochromic normoblast (metarubricyte). Nucleated RBCs falsely raise manual white blood cell (WBC) counts, which requires a manual WBC count correction.

nucleolus  Round or irregular pocket of messenger and ribosomal RNA in the nucleus. Nucleoli are observed by morphologists and are used to distinguish cell differentiation stages.

nucleoside  Glycoside of purine and pyrimidine bases. In RNA and DNA, the glycosides are the pentoses ribose and deoxyribose.

nucleotide  Phosphoric ester of a nucleoside. Allows for the formation of phosphodiesterase bridges between nucleotides to form RNA and DNA.

nucleus  Cellular organelle containing DNA and RNA. Stores genetic information and controls cell functions.

nucleus-to-cytoplasm (N:C) ratio  Estimated volume of a Wright-stained nucleus in comparison to the volume of the cytoplasm. The nucleus-to-cytoplasm ratio is used to differentiate cell developmental stages.

numerical aperture (NA)  Number stamped on the barrel of a microscope lens designating the quality of the microscope objective. The higher the number, the greater the lens’s resolution.

objective  Microscope lens closest to the specimen. Most clinical grade microscopes provide 10× dry, 50× oil immersion, and 100× oil immersion objectives.

ocular  Microscope lens, usually 10×, nearest the eye.

oncogene  Gene capable, under certain conditions, of causing the initial and continuing conversion of normal cells into cancer cells. A mutated proto-oncogene.

opsonization  Process by which an antibody or complement attaches itself to foreign material (bacteria), triggering or enhancing phagocytosis by white blood cells.

optical scatter  Scattering of light caused by the interaction of absorption, diffraction, refraction, and reflection. Hematology analyzers that use both laser and nonlaser light apply the principle of light scatter to perform cell counting and identification. The angle of light scatter correlates with various cell features such as volume, density, and cellular complexity.

orthochromic normoblast (metarubricyte)  Fourth stage of bone marrow erythropoiesis and the last in which the cell retains a nucleus. The nucleus is fully condensed with no parachromatin; the cytoplasm is 85% hemoglobinized and bluish-pink. When an orthochromic normoblast appears in the peripheral blood, it is called a nucleated red blood cell.

osmotic fragility test  Assay in which whole blood is pipetted to each of a series of saline solutions of graduated concentration. The series begins with water and increases in concentration to normal (0.85%) saline. The osmotic fragility test is used to detect spherocytosis, because spherocytes rupture in saline concentrations near the normal level. It may also detect target cells, which, owing to their reduced hemoglobin content, are able to withstand osmotic stress and rupture only at very dilute saline concentrations.

osteoblast  Bone-forming cell.

osteoclast  Large multinuclear cell associated with the absorption and removal of bone. May be confused with a megakaryocyte.

oval macrocyte  Oval red blood cell with an increased diameter seen in peripheral blood. Characteristic of megaloblastic anemia.

ovalocyte (elliptocyte)  Oval red blood cell seen in peripheral blood in the membrane disorder hereditary elliptocytosis. May be found in low numbers in healthy states and in other anemias such as iron deficiency and thalassemia major.

oxygen affinity  Ability of hemoglobin to bind oxygen molecules.

oxygen dissociation curve  Graphic expression of the affinity between oxygen and hemoglobin or the concentration of oxygen bound at equilibrium to the hemoglobin in blood as a function of oxygen pressure.

oxyhemoglobin  Hemoglobin that contains bound oxygen.

P arm  Smaller (petite) arm of a chromosome.

packed cell volume (PCV, hematocrit, HCT)  Proportion of whole blood that consists of red blood cells, expressed as a percentage of the total blood volume.

pallor  Unnatural paleness or absence of color from the skin.

pancytopenia  Marked reduction in the count of red blood cells, white blood cells, and platelets in peripheral blood.

Pappenheimer bodies (siderotic granules)  Red blood cell inclusions composed of ferric iron. On Prussian blue iron stain preparations, they appear as multiple dark blue irregular granules. On Wright stain preparations they appear as pale blue clusters.

parachromatin  Pale-staining portion of the nucleus, roughly equivalent to euchromatin.

parenteral  Pertaining to administration of drugs or other compounds by means other than oral administration; includes intramuscular and intravenous administration.

paroxysmal cold hemoglobinuria (PCH)  Rare acquired autoimmune hemolytic anemia in which the Donath-Landsteiner autoantibody binds red blood cells during exposure to cold, producing acute hemolysis and hematuria upon warming.

paroxysmal nocturnal hemoglobinuria (PNH)  Acquired hemolytic anemia due to a stem cell clonal mutation that causes the cell to lack glycosylphosphatidylinositol-anchored proteins, including CD55 and CD59, two proteins that normally protect the red blood cell (RBC) from complement activation and hemolysis. RBCs therefore have an increased susceptibility to complement, which results in intravascular hemolysis and hemoglobinuria that occur in irregular episodes.

partial thromboplastin time (PTT, activated partial thromboplastin time, APTT)  Clot-based screening test for intrinsic coagulation, which is prolonged in deficiencies of prekallikrein, high-molecular-weight kininogen, and factors XII, XI, IX, VIII, X, V, II, and fibrinogen. Calcium chloride, phospholipid, and activator are added to patient plasma. The interval from the addition of reagent to clot formation is recorded. The test is used to monitor unfractionated heparin therapy, to screen for intrinsic pathway deficiencies, and to screen for lupus anticoagulant.

pathogenesis  Chemical and biologic events in cells and tissue by which disease occurs and progresses.

pathognomonic  Specifically characteristic of a given disease; indicating a sign or symptom from which a diagnosis can be made.

Pelger-Huët anomaly  Autosomal dominant asymptomatic anomaly of neutrophil nuclei, which fail to segment and appear dumbbell shaped or peanut shaped (“pince-nez” nuclei). Pelgeroid nuclei are more common and resemble the nuclei of Pelger-Huët anomaly, but may indicate myelodysplasia or may appear during chemotherapy.

percutaneous coronary intervention (PCI)  Any catheter-based technique for the management of coronary artery occlusion, such as angiography, angioplasty, stent placement within a coronary artery, or cardiac catheterization.

peripheral artery occlusion (PAO)  Blockage of a noncardiovascular, noncerebral artery—for example, a carotid or brachial artery—by thrombus formation.

pernicious anemia  Progressive autoimmune disorder that results in megaloblastic macrocytic anemia due to a lack of, or antibodies to, parietal cells or intrinsic factor essential for the absorption of vitamin B12.

personal protective equipment (PPE)  Clothing that is used to prevent blood or other potentially infectious biologic substances from contacting clothing, eyes, mouth, or mucous membranes. Includes, for example, gloves, fluid-impermeable laboratory coats, and eye protection.

petechiae  Pinpoint purple or red spots on the skin or mucous membranes, approximately 1 mm in diameter, indicating small bleeds within the dermal or submucosal layers. May indicate a systemic bleeding disorder.

phagocyte  Cell that is able to surround, engulf, and digest microorganisms and cellular debris. Macrophages and neutrophils are phagocytes.

phagocytosis  Ingestion of large particles or live microorganisms into a cell.

phagosome  Membrane-bound cytoplasmic vesicle in a phagocyte containing the phagocytosed material.

Philadelphia chromosome  Reciprocal translocation of the long arm of chromosome 22 to chromosome 9; definitive for the diagnosis of chronic myelogenous leukemia. The mutation results in the fusion of the BCR and ABL genes and abnormal tyrosine kinase production.

phlebotomy  Use of a needle to puncture a vein and collect blood.

phytohemagglutinin (PHA)  Lectin extracted from the red kidney bean that causes red blood cell agglutination by binding to N-acetyl-β-glucosamine. Also a mitogen that induces T-lymphocyte proliferation in culture.

pinocytosis  Cellular ingestion of small particles or liquids.

pitting  Removal by the spleen of material from within red blood cells (RBCs) without damage to the RBCs; for example, removal of nuclei or Howell-Jolly bodies.

plasma  Fluid portion of the blood in which the formed elements (white blood cells, red blood cells, and platelets) are suspended.

plasma cell  Fully differentiated B lymphocyte found in the bone marrow and lymphoid tissue, and occasionally in peripheral blood. It contains an eccentric nucleus with deeply staining chromatin and abundant dark blue cytoplasm. The Golgi apparatus produces a perinuclear halo due to its high lipid content. Plasma cells secrete antibody in the humoral immune response.

plasma frozen within 24 hours (FP24)  Plasma that is separated from whole-blood donations and frozen within 24 hours of collection. FP24 contains all of the plasma procoagulants and control proteins, including adequate levels of the labile factors V and VIII. FP24 is used for replacement therapy in acquired multiple-factor deficiencies or in single-factor deficiencies when factor concentrates are not available.

plasmin  Active form of plasminogen. Plasmin binds fibrin and, when activated by tissue plasminogen activator, digests fibrin to form fibrin degradation products in the fibrinolytic process.

plasminogen  Inactive (zymogen) plasma precursor of plasmin.

plasminogen activator  Substance that cleaves plasminogen and converts it into plasmin; includes urokinase, which is secreted by renal endothelial cells, and tissue plasminogen activator, which is secreted by all endothelia. Synthetic plasminogen activators are used therapeutically to clear coronary artery clots after acute myocardial infarction.

plasminogen activator inhibitor 1 (PAI-1)  Endothelial cell inhibitor of tissue plasminogen activator; controls fibrinolysis.

platelet (thrombocyte)  Smallest of the formed elements in blood; disk-shaped, 2 to 4 µm in diameter, nonnucleated cell formed in the bone marrow from the cytoplasm of megakaryocytes. Platelets trigger and control blood coagulation.

platelet adhesion  Platelet attachment to subendothelial collagen, part of a sequential mechanism leading to the initiation and formation of a thrombus or hemostatic plug. Platelet adhesion requires von Willebrand factor and platelet receptor glycoprotein Ib/IX/V.

platelet aggregation  Platelet-to-platelet binding, part of a sequential mechanism leading to the initiation and formation of a thrombus or hemostatic plug. Requires fibrinogen and platelet membrane receptor glycoprotein IIb/IIIa.

platelet factor 4 (PF4)  Protein released from platelet α-granules that binds and inhibits heparin. The heparin-PF4 complex is implicated in heparin-induced thrombocytopenia with thrombosis.

platelet-poor plasma (PPP)  Plasma centrifuged to achieve a platelet count of less than 10, 000/μL. PPP is required for all coagulation testing, and only PPP may be frozen.

platelet-rich plasma (PRP)  Plasma centrifuged at 50 xg to achieve a platelet count of 200, 000/μL to 300, 000/μL. Platelet-rich plasma is used for light-transmission platelet aggregometry.

platelet satellitosis (satellitism)  Antibody-mediated in vitro adhesion of platelets to segmented neutrophils. Occurs primarily in specimens anticoagulated with ethylenediaminetetraacetic acid (EDTA) and causes pseudothrombocytopenia.

pleomorphic  Occurring in various distinct forms; having the ability to exist in various forms and to change from one form to another.

pluripotential stem cell  Stem cell that has the potential to differentiate into one of several types of hematopoietic progenitor cells, including lymphocytic, monocytic, granulocytic, megakaryocytic, and erythrocytic lineages and nonhematopoietic cells.

pneumatic tube system  System of tubes for transporting blood specimens or other small materials in hospitals by forced air.

poikilocytosis  Presence in the peripheral blood of red blood cells with varying or bizarre shapes.

point-of-care (POC) testing  Rapid-turnaround clinical tests performed outside of the clinical laboratory at or near the patient; usually performed by nonlaboratory personnel but managed for quality by laboratory personnel.

polychromatic (polychromatophilic)  Having a staining quality in which both acid and basic stains are incorporated. Usually used to denote a mixture of pink and blue in the cytoplasm of Wright-stained cells.

polychromatic normoblast (polychromatophilic normoblast, rubricyte)  Precursor in the erythrocytic maturation series, intermediate between the basophilic normoblast (prorubricyte) and the orthochromic normoblast (metarubricyte). In this stage, differentiation is based on the decreasing cell diameter and the gray-blue cytoplasm as hemoglobin first becomes visible.

polychromatic or polychromatophilic red blood cell (reticulocyte)  Immature but anucleate red blood cell (RBC) with bluish-pink cytoplasm on a Wright-stained blood film. When new methylene blue dye is used, the cytoplasm of these cells has a meshlike pattern of dark blue threads and particles, vestiges of the endoplasmic reticulum. Reticulocytosis or polychromatophilia indicates bone marrow regeneration activity in hemolytic anemia or acute blood loss.

polychromatophilia (reticulocytosis)  Elevated reticulocyte count on a peripheral blood film stained with new methylene blue dye or increase in the number of polychromatophilic red blood cells on a Wright-stained blood film. Reticulocytosis or polychromatophilia indicates bone marrow regeneration activity in hemolytic anemia or acute blood loss.

polyclonal  Describes a group of cells or organisms derived from several cells. Each cell is identical to its parent cells (i.e., a clone), but since all cells of the group did not derive from the same cell, the group of cells is mixed. A polyclonal antibody is developed within a laboratory animal and not a hybridoma.

polycythemia (erythrocytosis)  Elevated red blood cell count, hemoglobin, and hematocrit in peripheral blood, usually in response to chronic hypoxia.

polycythemia vera (PV)  Myeloproliferative neoplasm in which a somatic mutation leads to a marked increase in the red blood cell (RBC) count, hematocrit, hemoglobin, white blood cell count, platelet count, and red blood cell mass. RBC precursors are hypersensitive to erythropoietin.

polymerase chain reaction (PCR)  Laboratory process in which a strand of DNA is replicated in a thermocycler to produce millions of copies within a few hours.

polymorphonuclear neutrophil (PMN, segmented neutrophil, seg)  White blood cell whose nucleus is condensed into two to five segments or lobes connected by filaments. Distinguished from mononuclear cells such as monocytes and lymphocytes.

polyploid  Having more than the characteristic diploid set of chromosomes; for example, triploid (3×) or tetraploid (4×).

porphyria  Hereditary anemia caused by impaired heme synthesis with the accumulation of porphyrin and its precursors. Acquired porphyria may be seen in acute lead poisoning.

porphyrin  Product of the metabolism of a group of iron- or magnesium-free pyrrole derivatives such as protoporphyrin and protoporphyrinogen that incorporates ferrous iron to form heme.

posttransfusion purpura  Antibody-induced thrombocytopenia in patients who have received multiple transfusions of red blood cells or platelet concentrate. Antibodies to donor platelets cross-react with patient platelets to cause potentially life-threatening thrombocytopenia.

postmenstrual age  Time elapsed between the first day of the mother’s last menstrual period and birth (gestational age) plus the time elapsed after birth (chronologic age). For example, a preterm infant born at a gestational age of 32 weeks who is currently 10 weeks old (chronologic age) would have a postmenstrual age of 42 weeks.

precision  Degree to which the results of replicate analyses of a sample parallel each other, often expressed as coefficient of variation or percent coefficient of variation.

precursor  Differentiating (immature) hematopoietic cell stage that is morphologically identifiable as belonging to a given cell line; for example, pronormoblasts (rubriblasts) are precursors of basophilic normoblasts (prorubricytes) in erythropoiesis. Precursor may also refer to the inactive zymogen forms of coagulation factors; for example, prothrombin is a precursor of thrombin.

preeclampsia  Pathologic condition of late pregnancy characterized by edema, proteinuria, and hypertension; may lead to eclampsia, which presents with seizures and is often fatal.

prekallikrein (PK, pre-K, Fletcher factor)  Member of the kinin inflammatory system that forms active kallikrein upon digestion by kininogen. Pre-K helps to trigger in vitro coagulation contact activation. Pre-K deficiency prolongs the partial thromboplastin time but has no clinical consequence.

primary hemostasis  First phase of hemostasis in which the blood vessels contract to seal the wound and platelets and von Willebrand factor fill the open space by forming a platelet plug.

primary standard  Reference material that is of fixed and known composition and is capable of being prepared in essentially pure form.

primer  Short piece of synthetic DNA complementary to a target DNA sequence. The primer acts as a point from which replication can proceed, as in a polymerase chain reaction.

procoagulant  Coagulation (clotting) factor. During the coagulation process, inactive procoagulants become activated to form serine proteases or cofactors and function together to produce a localized thrombus.

progenitor  Undifferentiated (immature) hematopoietic cell that is committed to a cell line but cannot be identified morphologically.

prolymphocyte  Developmental form in the lymphocytic series that is intermediate between the lymphoblast and the lymphocyte.

promegakaryocyte  Morphologically identifiable bone marrow cell stage that is intermediate between the megakaryoblast and the megakaryocyte.

promonocyte  Precursor in the monocytic series; the cell stage intermediate in development between the monoblast and the monocyte.

promyelocyte  Precursor in the granulocytic (myelocytic) series that is intermediate in development between a myeloblast and a myelocyte; contains primary granules.

pronormoblast (rubriblast)  Undifferentiated (immature) hematopoietic cell that is the most primitive morphologically identifiable precursor in the erythrocytic series; differentiates into the basophilic normoblast (prorubricyte).

prorubricyte (basophilic normoblast)  Second identifiable stage in bone marrow erythrocytic maturation; it is derived from the pronormoblast (rubriblast). Typically 10 to 15 µm in diameter, the prorubricyte has cytoplasm that stains dark blue with Wright stain.

prostaglandin (PG)  Any of a family of unsaturated 20-carbon fatty acids that are cleaved from cell membrane phospholipids and serve as intracellular activators and inhibitors. The prostaglandins include thromboxane A2, a platelet activator, and prostacyclin, a platelet inhibitor produced by endothelial cells.

protein C (PC)  Vitamin K–dependent coagulation control protein. A plasma serine protease activated by thrombin-thrombomodulin and stabilized by its cofactor, protein S, protein C inhibits coagulation by inactivating factors Va and VIIIa.

protein S (PS)  Vitamin K–dependent coagulation control protein. Serves as a stabilizing cofactor for protein C, enabling activated protein C, a serine protease, to inactivate factors Va and VIIIa.

proteins in vitamin K antagonism (PIVKA)  Name given to the forms of factors II, VII, IX, and X and proteins C, S, and Z that, under conditions of vitamin K absence or antagonism, lack a second glutamic acid carboxyl group as required for binding to Ca2+ and phospholipid. Also called des-γ-carboxyl coagulation factors. The des-γ-carboxyl forms of these factors cannot participate in coagulation reactions. Vitamin K antagonism is the basis for oral anticoagulant therapy with warfarin (Coumadin).

proteolytic  Pertaining to any substance that digests protein by hydrolyzing primary peptide bonds.

prothrombin (coagulation factor II)  Plasma precursor of the coagulation factor thrombin. It is converted to thrombin by activated factor X complexed to factor V.

prothrombin time (protime, PT)  Test to measure the activity of coagulation factors I (fibrinogen), II (prothrombin), V, VII, and X, which participate in the extrinsic and common pathways of coagulation. Thromboplastin and calcium are added to plasma and the clotting time is recorded. Widely used to monitor warfarin therapy.

proto-oncogene  Normal gene controlling the cell cycle and other essential cell functions that, upon activation, may become an oncogene.

pseudo–Pelger-Huët cell (Pelgeroid cell)  Hyposegmented, hypogranular neutrophils that resemble Pelger-Huët cells. Helpful in the diagnosis of leukemia, myeloproliferative neoplasms, and myelodysplastic syndromes.

pseudoleukocytosis  Falsely increased white blood cell (WBC) count indicating mobilization of the marginal WBC pool caused by strenuous physical activity, cold, or fever. Also a falsely elevated WBC count due to interferences such as platelet clumping or lysis-resistant red blood cells.

pseudothrombocytopenia  Falsely decreased platelet count often caused by platelet satellitosis.

pulmonary embolism (PE)  Pathologic movement of a proximal fragment of clot from a deep vein thrombosis through the right side of the heart to the pulmonary circulation, where it lodges in an artery and causes infarction of the lung. Approximately one third of pulmonary emboli are fatal within 1 hour.

purpura  Purple skin discoloration, typically rounded with a diameter greater than 3 mm, seen in mucocutaneous bleeding. Usually seen in thrombocytopenia, platelet disorders, von Willebrand disease, or vascular disorders such as scurvy.

pyknosis  Degeneration of a cell in which the nucleus shrinks in size and the chromatin condenses to a solid, structureless mass or masses. Part of the process of apoptosis, or indicative of the effects of chemotherapy.

pyropoikilocytosis (hereditary pyropoikilocytosis)  Rare hereditary defect of spectrin that causes severe hemolytic anemia beginning in childhood with extreme poikilocytosis in which the red blood cell morphology resembles that seen in burn patients.

pyruvate kinase (PK)  Enzyme that converts phosphoenolpyruvate to pyruvate generating two molecules of ATP; essential for aerobic and anaerobic glycolysis.

pyruvate kinase deficiency  Autosomal recessive disorder resulting in a deficiency of pyruvate kinase, the enzyme that converts phosphoenolpyruvate to pyruvate; causes hemolytic anemia by reducing red blood cell life span. It is the most common enzyme deficiency of the Embden-Meyerhof pathway.

Q arm  Long arm of a chromosome.

Q banding (quinacrine banding)  In cytogenetic analysis, a procedure in which metaphase chromosomes are stained with fluorescent quinacrine dye. The areas rich in adenine-thymine, called Q+, fluoresce intensely, whereas the areas rich in guanine-cytosine (Q–) fluoresce more lightly. The Q+ bands correspond with G bands in Giemsa stain–based G banding. Banding patterns are used to identify chromosomes.

qualitative analysis  Study of a sample to determine the presence, but not the concentration, of specific chemicals.

quality control  Term used to refer to the control and monitoring of the testing process to ensure that the results are valid and reproducible.

quantitative analysis  Determination of the concentration of an analyte.

radiotherapy  Treatment of neoplastic disease using x-rays or gamma rays to deter the proliferation of malignant cells by disrupting mitosis or impairing DNA synthesis.

Raynaud phenomenon (acrocyanosis)  Persistent symmetrical cyanosis (blotchy blue or red discoloration) of the skin of the digits, palm, wrists, and ankles upon prolonged exposure to cold.

reactive lymphocytes (atypical, transformed, or variant lymphocytes)  Lymphocytes whose altered morphology includes stormy blue cytoplasm and lobular or irregular nuclei. Variant lymphocytes indicate stimulation by a virus, particularly Epstein-Barr virus, which causes infectious mononucleosis.

recessive  Denoting an allele whose product or effect is masked by a dominant allele at the corresponding locus. When an individual has two recessive genes, he or she is homozygous recessive, and the trait is expressed.

red blood cell (RBC) indices  Numerical representations of average RBC volume (mean cell volume), hemoglobin mass (mean cell hemoglobin), and relative hemoglobin concentration (mean cell hemoglobin concentration). Indices are computed from the RBC count, hemoglobin, and hematocrit values. The mean cell volume is directly measured by some hematology analyzers.

red cell distribution width (RDW)  Coefficient of variation of red blood cell volume. An increased red cell distribution width indicates anisocytosis.

red marrow  Hematopoietic bone marrow, in contrast to yellow, fatty bone marrow.

Reed-Sternberg cell  Giant, typically binucleate cell whose halves are mirror images. The nuclei are enclosed in abundant cytoplasm and contain prominent nucleoli. The presence of Reed-Sternberg cells is the definitive histologic characteristic of Hodgkin disease.

reference interval (RI)  Range of test results for a given analyte that is seen in a healthy population of individuals, typically computed as the mean plus or minus two times the standard deviation. Each laboratory must define the reference interval for the instrument that is being used and for the population that is being served.

refractive index  Speed at which light travels in air, divided by the speed at which light travels through another medium, such as immersion oil. The refractive index of oil is similar to the refractive index of glass.

reliability  Extent to which a method is able to maintain both accuracy and precision over a defined period of time.

remission  Partial or complete disappearance of the clinical and laboratory characteristics of a chronic or malignant disease.

replication  DNA duplication or synthesis prior to mitosis; may also be used to refer to mitosis.

reptilase  Thrombin-like enzyme isolated from the venom of Bothrops atrox that catalyzes the conversion of fibrinogen to fibrin in a manner similar to thrombin.

resheathing device  Device that allows safe one-handed recapping of a blood collection needle to prevent needle stick injury.

resolution  In microscopy, the smallest distance between which two adjacent objects can be distinguished. A measure of image and lens quality that relates to the smallest feature that can be seen with a set of lenses.

restriction endonuclease  Enzyme that cleaves DNA at a specific nucleotide site.

reticulocyte (polychromatic or polychromatophilic red blood cell)  Immature but anucleate red blood cell (RBC) that shows a meshlike pattern of dark blue threads and particles, vestiges of the endoplasmic reticulum, when stained with new methylene blue vital dye. In a Wright-stained blood film, no filaments are seen but the cytoplasm stains bluish-pink and the cell is called a polychromatic or polychromatophilic RBC.Reticulocytosis or polychromatophilia indicates bone marrow regeneration activity in hemolytic anemia or acute blood loss.

reticulocyte production index (RPI)  Index calculated to correct for the presence of shift reticulocytes that otherwise may falsely elevate the visual reticulocyte count.

reticulocytosis (polychromatophilia)  Elevated reticulocyte count on a peripheral blood film stained with new methylene blue dye or increase in the number of polychromatophilic red blood cells on a Wright-stained blood film. Reticulocytosis or polychromatophilia indicates bone marrow regeneration activity in hemolytic anemia or acute blood loss.

reticuloendothelial system (RES)  System of fixed and motile phagocytic macrophages and their precursor monocytes engaged in primary efferent immunity. Macrophages are found in every organ and tissue.

retrovirus  Any of a family of RNA viruses containing the enzyme reverse transcriptase.

reverse transcription polymerase chain reaction (RT-PCR)  Polymerase chain reaction amplification process that produces complementary DNA from the messenger RNA present in an RNA sample extracted from patient cells.

Rh immune globulin (RhIg)  Solution containing antibodies specific for the Rh(D) antigen given intramuscularly to an Rh(D)-negative mother with an Rh(D)-positive fetus or infant to prevent sensitization of the mother to the infant’s D antigen. It is given antepartum at 28 weeks’ gestation and again within 72 hours of delivery.

Rh-null disease  Hemolytic anemia in persons who lack all Rh antigens (Rh null); marked by spherocytosis, stomatocytosis, and increased osmotic fragility.

ribonucleic acid (RNA)  Single strand of polynucleotides connected by ribose molecules. RNA base sequences are transcribed from DNA and are the basis for translation to proteins. Major types of RNA include messenger RNA, ribosomal RNA, and transfer RNA.

ribosomes  Granules embedded in the membranes of endoplasmic reticulum that are composed of protein and RNA. Ribosomes are the sites for primary protein translation from messenger and transfer RNA.

ring sideroblast  Nucleated red blood cell precursor with at least five iron granules that circle at least one third of the nucleus. These cells, visible with Prussian blue stain, are the pathognomonic finding in refractory anemia with ring sideroblasts.

ristocetin  Antibiotic no longer in clinical use that facilitates the in vitro interaction of von Willebrand factor with platelet membrane glycoprotein Ib/IX/V. Used as an agonist in platelet aggregation to test for von Willebrand disease.

Romanowsky stain  Prototype of the many eosin–methylene blue stains for blood cells and malarial parasites, including Wright and Giemsa stain.

rouleaux  Aggregation of stacked red blood cells caused by elevated plasma proteins and abnormal monoclonal proteins.

rubriblast (pronormoblast)  Undifferentiated (immature) hematopoietic cell that is the most primitive morphologically identifiable precursor in the erythrocytic series; differentiates into the basophilic normoblast (prorubricyte).

rubricyte (polychromatic or polychromatophilic normoblast)  Precursor in the erythrocytic maturation series that is intermediate between the basophilic normoblast (prorubricyte) and the orthochromic normoblast (metarubricyte). In this stage, differentiation is based on the decreasing cell diameter and the gray-blue cytoplasm as hemoglobin first becomes visible.

Russell bodies  Plasma cell cytoplasmic inclusions that appear similar to vacuoles containing aggregates of immunoglobulins. Plasma cells with Russell bodies are called Mott cells.

Russell viper venom time  Rarely used coagulation assay similar to the prothrombin time. Russell viper venom activates the coagulation factor common pathway at the level of factor X. The dilute Russell viper venom time assay is used routinely in lupus anticoagulant screening.

scatterplot  Plot on rectangular coordinates of paired observations of two random variables, with each observation plotted as one point on the graph; the scatter or clustering of points provides an indication of the relationship between the two variables. In hematology a typical scatterplot graphs cell volume against cytoplasmic complexity.

schistocyte (schizocyte)  Fragmented red blood cell characteristic of microangiopathic hemolytic anemia, severe burns, disseminated intravascular coagulation, and prosthetic mechanical trauma.

scurvy  Deficiency of vitamin C (ascorbic acid) causing connective tissue breakdown. Marked by weakness, anemia, spongy gums, and a tendency to mucocutaneous bleeding.

secondary hemostasis  Second phase of hemostasis involving the activation of plasma coagulation proteins to produce a fibrin clot.

secondary standard (calibrator)  Calibration material for which the analyte concentration has been ascertained by reference to a primary standard or by controlled reference assays.

segmented neutrophil (seg, polymorphonuclear neutrophil, PMN)  White blood cell whose nucleus is condensed into two to five segments connected by filaments. Distinguished from mononuclear cells such as monocytes and lymphocytes.

selectin  Any of a family of cell adhesion molecules that mediate the binding of white blood cells and platelets to the vascular endothelium.

senescent  Aging or growing old. A senescent red blood cell loses its deformability and is cleared by the spleen.

sensitivity  In laboratory testing, the conditional probability that a person with a given disease will be correctly identified as having it by a clinical test (i.e., diagnostic sensitivity). Also, the lowest level of a substance that can be detected by a laboratory test procedure (i.e., analytical sensitivity).

sepsis (septicemia)  Proliferation of pathologic organisms in the blood.

sequestration  Transfer of blood cells from the circulation into a limited vascular area, such as the spleen. Platelets may be sequestered, which results in a decrease in their circulating numbers.

serine protease  Any of a group of proteolytic enzymes of the trypsin family that include activated procoagulants (thrombin and factors VIIa, IXa, Xa, XIa, and XIIa) and activated inhibitors (antithrombin, activated protein C). Serine proteases are synthesized as inactive zymogens; activation occurs when the zymogen is cleaved at one or more specific sites by the action of another protease during the coagulation process.

serine protease inhibitor (serpin)  Plasma proteins, for instance, antithrombin and heparin cofactor II, which control the coagulation cascade by inhibiting the serine proteases, particularly factors IIa and Xa.

serotonin  Potent vasoconstrictor released from the dense granules of activated platelets.

Sézary cell  Mononuclear cell with a cerebriform nucleus (resembling the surface of the cerebrum) and a narrow rim of cytoplasm. It is a characteristic finding in cutaneous T-cell lymphomas.

Sézary syndrome  Cutaneous T-cell lymphoma characterized by exfoliative erythroderma, peripheral lymphadenopathy, and the presence of Sézary cells in the skin, lymph nodes, and peripheral blood.

shift reticulocyte  Gray-blue red blood cell with increased diameter. The shift reticulocyte is a reticulocyte that has been released from the bone marrow prematurely to compensate for hemolytic anemia or acute blood loss. Shift reticulocytes require more than 1 day in the peripheral blood to lose residual RNA and gain a mature-looking reddish cytoplasm.

sickle cell (drepanocyte)  Abnormal crescent-shaped red blood cell containing hemoglobin S, characteristic of sickle cell anemia.

sickle cell anemia (sickle cell disease)  Severe chronic hemoglobinopathy in people who are homozygous for hemoglobin S. The abnormal hemoglobin results in distortion of red blood cells (sickle cells) and leads to crises characterized by joint pain, anemia, thrombosis, fever, and splenomegaly.

sickle cell crisis  Any of several acute conditions occurring as part of sickle cell disease, such as aplastic crisis, which is temporary bone marrow aplasia; hemolytic crisis, which is acute red blood cell destruction; and vasoocclusive crisis, which is severe pain due to blockage of the blood vessels.

sickle cell trait  Asymptomatic heterozygous condition characterized by the presence of both hemoglobin S and hemoglobin A.

sideroblast  Bone marrow erythrocytic precursor that shows excessive iron granules (siderotic granules) with Prussian blue staining.

siderocyte  Nonnucleated red blood cell in which particles of iron (siderotic granules) are visible with Prussian blue staining.

siderotic granules (Pappenheimer bodies)  Red blood cell inclusions composed of ferric iron. With Prussian blue iron staining, they appear as multiple dark blue irregular granules. With Wright staining they appear as pale blue clusters.

Southern blotting  Technique in which DNA fragments separated by gel electrophoresis are transferred to a nitrocellulose filter on which specific fragments can then be detected by their hybridization to probes.

specificity  In laboratory testing, the conditional probability that a person who does not have a specific disease will be correctly identified as not having it by a clinical test (i.e., diagnostic specificity). Also used to describe the attribute of antibodies that are able to bind only with the antigen that stimulated their production.

spectrin  Major cytoskeletal protein forming a lattice at the cytoplasmic surface of the cell membrane, providing lateral support to the membrane and thus maintaining its shape. Abnormalities in red blood cell spectrin account for hereditary spherocytosis, ovalocytosis, and pyropoikilocytosis.

spherocyte  Abnormal spherical red blood cell with a decreased surface area-to-volume ratio. In Wright-stained peripheral blood films, spherocytes are dense, lack central pallor, and have a reduced diameter. Spherocytes appear most frequently in warm autoimmune hemolytic anemia and hereditary spherocytosis.

spleen  Large organ in the upper left quadrant of the abdomen, just under the stomach. The spleen has the body’s largest collection of macrophages, which are responsible for phagocytosis and elimination of senescent red blood cells. The spleen also houses many lymphoid cells.

splenectomy  Excision of the spleen.

splenomegaly  Enlargement of the spleen.

standard deviation  Mathematic expression of the dispersion of a set of values or scores about the mean.

standard precautions (universal precautions)  Practices to control blood-borne disease in which all human blood and body fluids are treated as if infectious. Infection is prevented by a series of protective methods including the use of sterile gloves, fluid-impermeable clothing, and eye protection.

steatorrhea  Fat in the stool, usually due to malabsorption. Stool is green or colorless and foul smelling.

stem cell  Undifferentiated mononuclear cell whose daughter cells may give rise to a variety of cell types and which is capable of renewing itself and thus maintaining a pool of cells that can differentiate into multiple other cell types.

stomatocyte  Abnormal cup-shaped mature red blood cell that has a slitlike area of central pallor.

storage pool deficiency  Inadequacy of platelet dense granules or dense granule contents that causes mucocutaneous bleeding. Usually hereditary and related to conditions with oculocutaneous albinism, such as Hermansky-Pudlak syndrome, Chédiak-Higashi syndrome, and Wiskott-Aldrich syndrome. Acquired storage pool disorder is sometimes associated with myelodysplastic syndrome.

stroma  Supporting tissue or matrix of an organ.

subcutaneous (SC)  Injected within the subdermal or dermal layer.

sulfhemoglobin  Hemoglobin with a sulfur atom on one of its porphyrin rings, which makes it ineffective for transporting oxygen. Results from ingestion or exposure to drugs or chemicals containing sulfur.

supernatant  Clear upper liquid part of a suspension after it has been centrifuged.

suppuration  Formation or discharge of pus.

supravital stain (vital stain)  Stain that colors living tissues or cells.

surface-connected canalicular system (SCCS, open canalicular system, OCS)  System of channels that is distributed throughout platelets and extends the plasma membrane inward. The SCCS binds numerous coagulation factors and provides a route for secretion of the protein contents of α-granules.

syncope  Brief lapse in consciousness; fainting.

systemic bleeding disorder  Chronic episodic bleeding that is evidenced by bilateral petechiae and purpura, epistaxis, hematemesis, and menorrhagia. Indicates a primary coagulopathy such as thrombocytopenia, von Willebrand disease, or a qualitative platelet disorder.

systemic lupus erythematosus (SLE)  Chronic autoimmune inflammatory disease manifested by severe vasculitis, renal involvement, and lesions of the skin and nervous system.

T cell (T lymphocyte)  Lymphocyte that participates in cellular immunity, including cell-to-cell communication. The major T-cell categories are helper cells and suppressor-cytotoxic cells.

target cell (codocyte)  Poorly hemoglobinized red blood cell (RBC) that is present in hemoglobinopathies, thalassemia, and liver disease. In a Wright-stained peripheral blood film, hemoglobin concentrates in the center of the RBC and around the periphery to resemble a “bull’s-eye.”

teardrop cell (dacryocyte)  Red blood cell with a single pointed extension, resembling a teardrop. Dacryocytes are often seen in the myeloproliferative neoplasm called myelofibrosis with myeloid metaplasia.

telangiectasia  Permanent dilation of capillaries, arterioles, and venules that creates focal red lesions, usually in the skin or mucous membranes.

telomere  Repeating DNA sequences at a chromosome terminus.

tetraploid  Possessing a double diploid chromosome complement, or four of each chromosome (4N).

thalassemia  Production and hemolytic anemia characterized by microcytic, hypochromic red blood cells caused by deficient synthesis of α- or β-globin chains.

thrombin  Primary serine protease of coagulation. Factors Xa and Va combine to cleave prothrombin to produce thrombin. Thrombin cleaves fibrinopeptides A and B from fibrinogen to initiate fibrin polymerization. Thrombin potentiates coagulation by activating platelets and factors XI, VIII, V, and XIII and also activates the coagulation control protein, protein C.

thrombin clotting time (TCT, thrombin time, TT)  Coagulation test that measures the interval to clot formation after the addition of thrombin to plasma. Often used to test for the presence of heparin.

thrombocyte  Platelet.

thrombocythemia  Abnormally high platelet count with dysfunctional platelets; seen in the myeloproliferative neoplasm known as essential thrombocythemia.

thrombocytopenia  Platelet count below the lower limit of the reference interval, usually 150, 000/μL.

thrombocytosis  Platelet count above the upper limit of the reference interval, usually 450, 000/μL.

thrombophilia (hypercoagulability)  Abnormally increased tendency to clotting caused by a number of acquired or congenital factors.

thrombopoietin  Hormone produced by renal tissue that recruits stem cells to the megakaryocyte cell maturation line and stimulates megakaryocyte mitosis and maturation in response to thrombocytopenia.

thrombosis  Formation, development, or presence of a clot in a blood vessel (i.e., a thrombus).

thrombospondin  Adhesive glycoprotein secreted by endothelial cells and platelet α-granules.

thrombotic thrombocytopenic purpura (TTP)  Congenital or acquired deficiency of ADAMTS-13, an endothelial cell von Willebrand factor–cleaving protease. Ultra-large von Willebrand factor multimers activate platelets to form white clots in the microvasculature, causing severe thrombocytopenia with mucocutaneous bleeding, microangiopathic hemolytic anemia, and neuropathy.

thromboxane A2  Metabolically active product of the eicosanoid synthesis (cyclooxygenase, prostaglandin) pathway in platelets; binds platelet membrane receptor and activates platelets.

thromboxane B2  Metabolically inactive measurable plasma product of the eicosanoid synthesis (cyclooxygenase, prostaglandin) pathway.

thrombus  In vivo blood clot causing vascular occlusion and tissue ischemia.

tissue factor (TF)  Constitutive membrane protein of the subendothelium. Exposure to tissue factor activates factor VII and the tissue factor (extrinsic) coagulation pathway. Tissue factor is expressed on monocytes and endothelial cells in chronic inflammation.

tissue plasminogen activator (TPA)  Serine protease that is secreted by endothelial cells and binds fibrin. It activates nearby plasminogen molecules to trigger fibrinolysis, with the formation of fibrin degradation products.

toxic granulation  Presence of abnormally large, dark-staining, or dominant primary granules in neutrophils associated with bacterial infections.

transcription  Process by which messenger RNA is produced from a DNA template.

transferrin  Plasma iron-transport protein that moves iron from sites of absorption and storage to hematopoietic tissue for incorporation into developing normoblasts.

transformed lymphocytes (atypical, variant, or reactive lymphocytes)  Lymphocytes whose altered morphology includes stormy blue cytoplasm and lobular or irregular nuclei. Variant lymphocytes indicate stimulation by a virus, particularly Epstein-Barr virus, which causes infectious mononucleosis.

translation  Process by which the genetic information carried by nucleotides in messenger RNA directs the sequence of amino acids in the synthesis of a specific polypeptide.

translocation  Rearrangement of DNA within a chromosome or transfer of a segment of one chromosome to a nonhomologous one.

triploid  Possessing a single addition chromosome complement, resulting in three of each chromosome (3N).

trisomy  Presence of an extra chromosome in addition to a homologous pair; for example, trisomy 21 in Down syndrome.

tungsten-halogen light bulb  Bulb used in brightfield microscopy consisting of a tungsten filament enclosed in a small quartz bulb filled with halogen gas. Tungsten creates a very bright yellow light.

unfractionated heparin (UFH, standard heparin)  Heparin extracted from porcine mucosa and purified to yield molecular weights ranging from 7000 to 15, 000 Daltons. Used routinely in cardiac surgery. Unfractionated heparin therapy requires monitoring with the partial thromboplastin time or activated clotting time assay.

universal precautions (now called standard precautions)  Practices to control blood-borne disease in which all human blood and body fluids are treated as if infectious. Infection is prevented by a series of protective methods including the use of sterile gloves, fluid-impermeable clothing, and eye protection.

urobilinogen  Colorless water-soluble compound formed in the intestine through the breakdown of bilirubin by bacteria; low levels appear in the urine in healthy states.

urokinase  Enzyme produced by the kidney endothelial cells that acts as a plasminogen activator.

vacuole  Any clear space or cavity formed in the cytoplasm of a cell.

vacuolization  Formation of vacuoles.

vasoconstriction  Reduction in blood vessel diameter due to smooth muscle constriction.

venipuncture  Use of a needle to puncture a vein and collect blood.

vertigo  Sensation of rotation or movement of oneself or one’s surroundings; dizziness.

viscosity  Resistance of a liquid to flow.

vital stain (supravital stain)  Stain that colors living tissues or cells.

vitamin B12 (cyanocobalamin)  Complex vitamin involved in the metabolism of protein, fats, and carbohydrate; normal blood formation; and nerve function.

vitamin K  Natural phylloquinone occurring in green leafy vegetables and liver and produced by commensal intestinal organisms. Vitamin K catalyzes the γ-carboxylation of glutamic acid in a number of calcium-binding proteins, including the vitamin K–dependent coagulation proteins factors II (prothrombin), VII, IX, and X and control proteins C, S, and Z.

vitamin K antagonist (VKA)  Substance that inhibits the action of vitamin K; for example, warfarin (Coumadin), which is used in oral anticoagulant therapy.

von Willebrand disease  Congenital autosomal dominant variable mucocutaneous bleeding disorder characterized by a deficiency of von Willebrand factor activity and antigen, and subsequent impairment of platelet adhesion.

waived testing  Test classification defined by the Clinical Laboratory Improvement Amendments that includes tests that are simple and accurate and can be performed by noncertified personnel.

Waldenström macroglobulinemia  Form of monoclonal gammopathy in which IgM is overproduced by the clone of a plasma cell. Increased viscosity of the blood may result in circulatory impairment, and normal immunoglobulin synthesis is decreased, which increases susceptibility to infections.

warfarin (Coumadin)  Vitamin K antagonist used as an anticoagulant to prevent thrombosis in people with atrial fibrillation, venous thromboembolism, or cardiac insufficiency. Also used prophylactically after orthopedic surgery. Warfarin suppresses vitamin K and reduces the activity of the vitamin K–dependent coagulation factors II (prothrombin), VII, IX, and X.

warm antibody  IgG antibody that reacts optimally at a temperature of 37° C.

warm autoimmune hemolytic anemia  Most common autoimmune hemolytic anemia, which results from the reaction of IgG autoantibodies with red blood cells at an optimal temperature of 37° C.

Wiskott-Aldrich syndrome  Immunodeficiency disorder characterized by oculocutaneous albinism, thrombocytopenia, inadequate T- and B-cell function, and an increased susceptibility to viral, bacterial, and fungal infections.

xanthochromic  Having a yellowish color. Used to describe cerebrospinal fluid, in which xanthochromia indicates the presence of bilirubin and thus serves as evidence of a prior episode of bleeding into the brain.

X-linked  Pertaining to genes or to the characteristics or conditions they transmit that are carried on the X chromosome.

X-linked recessive inheritance  Pattern of inheritance in which a recessive allele is carried on the X chromosome; results in the carrier state in females and development of disease characteristics in males, since they do not have a normal X chromosome to compensate.

zymogen  Inactive precursor that is converted to an active form by an enzyme. Zymogens are inactive coagulation factors, such as prothrombin.