Wendy N. Erber
Synopsis
Disorders of red blood cells may be due to reduced or excessive production in the bone marrow, premature cell destruction (haemolysis) or loss from the circulation. A precise diagnosis must be made from the blood count, blood film, biochemistry and/or bone marrow examination so that appropriate therapy can be instituted. Anaemia due to a haematinic deficiency can be treated with specific replacement therapy (e.g. iron, vitamin B12 or folic acid) along with management of the underlying cause. Other secondary anaemias may benefit from haemopoietic growth factor therapy such as erythropoiesis-stimulating agents (e.g. for chronic renal disease), immunosuppression (e.g. for autoimmune haemolytic) or avoidance of specific drugs (e.g. sulfonamides or antibiotics). Over-production of red cells, as in polycythaemia vera, is managed by venesection and, for some patients, suppressing marrow erythropoiesis.
• Iron.
• Vitamin B12.
• Folic acid.
• Haemolytic anaemia.
• Haemoglobinopathies.
• Aplastic anaemia.
• Polycythaemia vera.
• Haemopoietic growth factors.
Iron
Iron is a trace element that is required for oxygen transport by erythrocytes and for oxidative metabolism in all cells. Up to 75% of body iron is present in haemoglobin (Hb), and the majority of the remainder in myoglobin and enzymes. A normal daily diet contains approximately 10–20 mg iron which is present in meat (heme iron), grains and vegetables. Only 5–10% of dietary iron is absorbed which is sufficient to compensate for the normal daily loss of iron (1 mg/day) in faeces and desquamation of skin. Iron requirements are greater during periods of growth (i.e. childhood), as a result of blood loss in menstruation (average menstrual cycle loses 10–15 mg iron) and increased requirements (e.g. pregnancy up to 3 mg iron/day). Gastrointestinal iron absorption can increase up to five-fold with increased demand. Ascorbate increases iron absorption.
Dietary iron is reduced to the ferrous (Fe2 +) state at the brush border of the duodenum. Divalent metal transport 1 (DMT1), located on the membrane of duodenal enterocytes, then transports iron across the intestinal lumen; this is aided by an acidic environment. Ferroportin, facilitated by hephaestin, then releases iron into the bloodstream. Hepcidin is a key regulator of iron homeostasis and directly inhibits ferroportin release of iron (Fig. 30.1). In the plasma, iron binds to transferrin and delivers it to transferrin receptors on developing erythroblasts in the bone marrow. Alternatively, iron may be stored intracellularly, or excreted in faeces from shed mucosal cells. After 120 days red cells die and the haemoglobin from senescent erythrocytes is released, phagocytosed by macrophages and exported by ferroportin back to plasma transferrin. Excess iron is stored in the bone marrow, hepatocytes and spleen as ferritin (20–300 μg/L).
Fig. 30.1 Iron homeostasis. At the brush border, dietary iron is reduced to the ferrous state by duodenal ferric reductase (Dcytb), transported into the mucosal cell by divalent metal transporter 1 (DMT1) and released via ferroportin into the circulation facilitated by hephaestin. Most absorbed iron is delivered to erythroid precursors. Hepatocytes take up iron from the circulation either as free iron or transferrin-bound iron via transferrin receptors 1 and 2. Hepcidin secretion by hepatocytes down-regulates ferroportin-mediated release of iron from enterocytes, macrophages and hepatocytes.
(Reproduced with permission from Fleming R E, Bacon B R 2005 Orchestration of iron homeostasis. New England Journal of Medicine 352:1741–1744.)
Iron deficiency
Case study
A 36-year-old mother of two children presents with shortness of breath on exertion, fatigue and menorrhagia. Her Hb is 6.4 g/dL with a mean cell volume of 72 fL (normal 80–100 fL). The blood film shows hypochromic microcytic red cells. Her ferritin is 2 μg/L (normal 20–200 μg/L). Iron deficiency anaemia secondary to blood loss is diagnosed. Although symptomatic she refuses transfusion therapy. Oral iron therapy is commenced with 200 mg ferrous sulphate (non-enteric coated) administered three times daily. She is referred to a gynaecologist for management of the menorrhagia. Iron therapy is prescribed for 3 months.
Iron deficiency is the commonest cause of anaemia worldwide. The major causes are:
• Inadequate dietary intake: young infants with inadequate intake of solids (18 months to 3 years), poverty and poor nutrition.
• Increased physiological iron requirements: increased iron demands for growth, i.e. prematurity, rapid growth in adolescence and pregnancy (especially third trimester).
• Reduced iron absorption: coeliac disease, post-gastrectomy and gluten-induced enteropathy.
• Blood loss: menstruation, menorrhagia, gastrointestinal malignancy, other causes of chronic haemorrhage (e.g. associated with salicylate and non-steroidal anti-inflammatory drugs), hookworm infection and chronic intravascular haemolysis.
The serum ferritin concentration correlates with body iron stores; serum ferritin of < 15 μg/L is virtually specific for iron deficiency. As ferritin is an acute-phase reactant, a normal result does not exclude iron deficiency in the presence of infective and inflammatory conditions. In the anaemia of chronic disease a ferritin < 50 μg/L may be associated with reduced storage iron, whereas ferritin levels of > 50 μg/L generally indicate the presence of iron stores. Measurement of serum soluble transferrin receptor (increased in iron deficiency but not by inflammation) may help in differentiating iron deficiency from the anaemia of chronic disease.
Management of iron deficiency and prophylactic iron administration
Management of iron deficiency requires:
1. identification and treatment of the underlying cause, and
2. iron replacement therapy.
Oral iron preparations are the treatment of choice due to their effectiveness, safety and low cost. Iron can be administered as simple iron salts (e.g. ferrous sulphate, fumarate or gluconate) or in saccharated form (Table 30.1). Administration of 200 mg ferrous sulphate three times daily provides 180 mg elemental iron per day; up to 30% of the orally administered iron will be absorbed. The haemoglobin will increase by 1 g in the first week; a rise of 2 g/dL after 3 weeks’ therapy is evidence of adequate response. Daily administration for 1–3 months will correct anaemia due to iron deficiency. Therapy should be continued for a further 3 months and until the haemoglobin has normalised and iron stores replenished (i.e. serum ferritin > 50 μ/L).
Table 30.1 Oral iron preparations
Liquid iron formulations can be used for small children but they stain the teeth. Formulations include ferrous sulphate solution (5 mL contains 12 mg elemental iron), iron polymaltose solutions and polysaccharide–iron complex (5 mL contains 100 mg elemental iron). Prophylactic oral iron is appropriate in pregnancy, menorrhagia, following partial or complete gastrectomy, for patients with chronic renal disease receiving erythropoietin, in the early treatment of severe pernicious anaemia (rapid erythropoiesis may exhaust iron stores) and for low-birth-weight or premature infants. Lower doses of oral iron (e.g. 200 mg ferrous sulphate daily) are generally prescribed.
Sustained or slow-release iron preparations have iron bound to resins, chelates (sodium feredetate) or plastic matrices (e.g. Ferrograd, Feospan). Iron is released in the lower small intestine and it has therefore bypassed the duodenum, the site of maximal iron absorption before becoming available. They are therefore relatively ineffective sources of iron and should not be used to treat iron deficiency. They cause fewer unwanted effects reflecting the small amount of iron absorbed.
Adverse effects of oral iron (e.g. nausea, epigastric pain, diarrhoea and constipation) are related to the amount of available iron. These effects can generally be ameliorated by reducing the dose, using divided doses, switching to an alternative iron salt (e.g. ferrous gluconate), and/or taking the iron with food. Although these approaches reduce the amount of iron available to be absorbed, the speed of normalisation of the haemoglobin concentration is not usually critical. Managing the gastrointestinal disturbance is important to ensure the patient continues treatment. Failure of oral iron therapy is most commonly due to poor compliance, persistent bleeding or incorrect diagnosis. Oral iron may not be well absorbed in patients who have had a partial or complete gastrectomy or coeliac disease. Folate deficiency may be unmasked by effective iron therapy. Where there is a deficiency of both iron and folate, the latter may not be obvious until iron is administered. This is most likely in pregnancy due to high fetal requirements for both haematinics.
Parenteral iron is rarely indicated and should only be administered if there is:
• Proven iron deficiency and oral iron cannot be tolerated.
• Ongoing blood loss so severe that oral therapy is insufficient to maintain iron stores.
• Inadequate gastrointestinal iron absorption.
Parenteral iron formulations include:
• Iron dextran (ferric hydroxide complexed with dextrans, 50 mg/mL) which can be administered by deep intramuscular injection, slow intravenous injection or infusion.
• Iron sucrose (ferric hydroxide complexed with sucrose, 20 mg/mL) which is delivered by slow intravenous injection or infusion (not recommended for children).
The dose of parenteral iron is based on body weight and the haemoglobin (Hb) deficit, as follows:
The speed of haemopoietic response is no faster with parenteral therapy than with full dose oral iron when reliably taken and normally absorbed. Parenterally administered iron is stored and utilised over months.
Adverse effects of intravenous iron include immediate, severe and potentially life-threatening anaphylactoid reactions, fever and arthropathy. Patients should therefore be closely monitored during administration and facilities for cardiopulmonary resuscitation should be available. A history of allergic disorders including asthma, eczema and anaphylaxis is a contraindication to parenteral iron. Intramuscular iron can be painful and may permanently stain the skin.1 Less severe manifestations include urticaria, rashes and nausea; delayed reactions such as arthralgia, myalgia and fever can also occur. Intramuscular iron has also been associated with soft tissue sarcomas. Oral iron preparations should not be given for 24 h prior to parenteral therapy or for 5 days after the last intravenous injection. This is to prevent adverse reactions as a result of saturation of transferrin binding capacity leading to a high, unbound plasma iron concentration.
Drug interactions
Iron chelates a number of drugs including tetracyclines, penicillamine, methyldopa, levodopa, carbidopa, ciprofloxacin, norfloxacin and ofloxacin, thereby reducing their absorption. Iron also forms stable complexes with thyroxine, captopril and bisphosphonates. Administration of these drugs should be separated from the iron therapy by a minimum of 2 h. Ascorbic acid increases iron absorption but its use is not clinically important in routine therapy. Antacids, tea (tannins) and bran reduce iron absorption.
Anaemia of chronic disease
Case study
A 54-year-old lady with active rheumatoid arthritis is noted to be anaemic (Hb 9.3 g/dL). Apart from her swollen and painful small joints she is asymptomatic. Her blood film shows normochromic normocytic red cells with a mild neutrophilia. Analysis of her iron status shows serum iron of 3 μmol/L (normal = 14–32), transferrin 1.5 g/L (normal = 2.0–3.6) and ferritin 250 μg/L (normal = 20–200). A diagnosis of anaemia of chronic disease is made. As she is asymptomatic from the anaemia, transfusions are not required and iron therapy is not indicated.
The anaemia of chronic disease occurs in response to chronic infective or inflammatory processes and malignancies and must be distinguished from iron deficiency. Increased hepcidin expression reduces intestinal iron absorption and increases iron stored in macrophages and hepatocytes. Serum iron is therefore reduced and ferritin normal or increased. The aim of therapy is to treat the underlying disorder, which generally is the cause of the patient's symptoms and not the anaemia per se. If the anaemia is sufficiently severe to impair quality of life, red cell transfusions may be indicated. Erythropoiesis-stimulating agents (ESA) generally do not give significant improvement in quality of life and can increase the risk of venous thromboembolic disease and mortality, especially in patients with malignant disease. Iron should not be given to patients with the anaemia of chronic disease as the abnormality is impaired iron utilisation and not iron deficiency.
Functional iron deficiency
Functional iron deficiency occurs when the iron demands of developing erythroblasts exceed the body's ability to deliver iron to the marrow. In the anaemia of chronic renal disease, for example, this impairment of iron delivery can limit the haemoglobin response to ESA therapy. This can be overcome with regular low dose intravenous iron administration (e.g. 100 mg iron sucrose monthly). The serum ferritin should be monitored to ensure it does not exceed 500–1000 μg/L.
Chronic iron overload
Severe tissue iron overload can result from excessive absorption (hereditary haemochromatosis), frequent or chronic red cell transfusion therapy (> 100 units as in thalassaemia or myelodysplasia2) leading to transfusion haemosiderosis and excessive parenteral iron therapy. Iron chelation is required to prevent irreversible end-organ (e.g. heart, liver) damage. In haemochromatosis iron is removed by weekly venesection (450 mL blood eliminates 200–250 mg iron) until the ferritin has normalised and thereafter, as required, to maintain the ferritin at < 50 μg/L.
Iron chelation therapy has been available since the 1970s and is used when venesection is contraindicated, most commonly for transfusion haemosiderosis. This is particularly for patients who are transfusion-dependent from infancy (e.g. thalassaemia major). In thalassaemia, iron chelation therapy is generally commenced after 1 year of monthly blood transfusions. In older transfusion-dependent patients with refractory anaemia (e.g. myelodysplasia), iron chelation is commenced after 20 transfusions or when the serum ferritin level is two to three times the upper limit of normal. Both parenteral and oral iron chelators are available.
Parenteral iron chelator
Desferrioxamine is administered by subcutaneous injection or intravenously (30–50 mg/kg/day) over an 8–12 h period, 5–7 nights per week. It has a half-life of 6 h. Compliance with therapy is a problem because of the slow parenteral administration. Desferrioxamine complexes with ferric iron to form ferrioxamine which is excreted in urine and in bile. Simultaneous administration of ascorbic acid should be avoided; although ascorbic acid increases the availability of free iron for chelation, it also mobilises iron from reticuloendothelial storage sites to a potentially toxic pool in parenchymal cells. Serious adverse effects of desferrioxamine are uncommon but do include anaphylactic reactions. Rapid infusion can result in hypotension, shock or urticaria. There is danger of potentially fatal adult respiratory distress syndrome if infusion proceeds beyond 24 h.3 Chronic use can result in hearing and visual disturbances (cataract and retinal damage).
Oral iron chelators
Orally absorbed iron chelators have become available in the past decade and give improved compliance and quality of life for those who require lifelong iron chelation. The two major products available are:
Deferiprone (3-hydroxy-1,2-dimethylpyridin-4-one). Deferiprone is an oral iron chelator that binds iron in a 3:1 molar ratio. It is administered 25 mg/kg three times daily. It can prevent iron accumulation but not necessarily protect against iron-induced organ damage. Deferiprone is absorbed in the upper gastrointestinal tract and is mainly excreted via the kidneys; the elimination half-life is 2–3 h. It is less effective than desferrioxamine and carries a risk of arthropathy, neutropenia and agranulocytosis. It is, however, a useful alternative for patients who are unwilling or unable to tolerate desferrioxamine. Combination therapy of deferiprone with desferrioxamine is effective in the management of cardiac siderosis.
Deferasirox. This is a tridentate oral iron chelator that mobilises stored iron by binding selectively to ferric iron. It provides 24 h chelation with a once-daily dose (20–30 mg/kg per day). It is effective in removing cellular (i.e. cardiac and hepatic) and serum iron, which it excretes in the faeces. Side-effects include gastrointestinal disturbances, skin rash, cytopenias and increased creatinine.
Iron poisoning and acute overdose
Iron poisoning is commonest in children, is usually accidental and particularly dangerous. The phases in acute oral iron poisoning are shown in Box 30.1. Ferrous sulphate is the most toxic, while sustained-release iron preparations and multivitamins cause less severe poisoning. Poisoning is severe if the plasma iron concentration exceeds the total iron binding capacity (upper limit 75 mmol/L) or plasma becomes pink due to the formation of ferrioxamine. Treatment is urgent and involves chelating iron in plasma. As an immediate measure, raw egg and milk help bind iron in the stomach. Iron chelation therapy is required for severe toxicity. Desferrioxamine is administered by intravenous infusion (not exceeding 15 mg/kg/h and maximum 80 mg/kg in 24 h) to chelate serum free iron.
Box 30.1 Acute Iron Poisoning
Phase 1
0.5–1 h after ingestion: Abdominal pain, grey-black vomit, diarrhoea, leucocytosis and hyperglycaemia. Severe cases have acidosis and cardiovascular collapse which may proceed to coma and death.
Phase 2
Improvement occurs, lasting 6–12 h; may be sustained or may deteriorate to next phase.
Phase 3
Jaundice, hypoglycaemia, bleeding, encephalopathy, metabolic acidosis and convulsions are followed by cardiovascular collapse, coma and sometimes death 48–60 h after ingestion. Severe brain and liver damage is seen at autopsy.
Phase 4
1–2 months later: scarring and stricture may cause upper gastrointestinal obstruction.
Vitamin B12
The cobalamins are a family of compounds (cyano-, hydroxyo-, methyl- and adenosylcobalamin) that have vitamin B12 activity. They have the same basic structure with cobalt within a central corrin ring. Vitamin B12 is produced only by microorganisms and humans obtain it by ingesting foods of animal origin. Vitamin B12 is required by all cells for DNA synthesis; it is also required for red cell production, methylation and myelin synthesis. A normal diet contains 5–30 μg vitamin B12 per day and 1–3 μg is absorbed. Ingested vitamin B12 binds to intrinsic factor (IF) synthesised by gastric parietal cells. The cobalamin–IF complex passes to the terminal ileum where it is absorbed. Newly absorbed vitamin B12 binds to transcobalamin to form holotranscobalamin (20–30% of plasma vitamin B12); this is the biologically active form which is available for delivery to cells. Most vitamin B12 (70%) in the blood is bound to haptocorrin (holohaptocorrin, formerly transcobalamin I) which is taken up by and stored in the liver. The liver stores up to 2–5 mg of vitamin B12, which is sufficient for 2–4 years after absorption ceases. Cobalamin is not metabolised significantly and passes into bile and urine.
Vitamin B12 deficiency
The causes of vitamin B12 deficiency are listed in Table 30.2. The most common are:
• Inadequate dietary intake: the elderly and vegans.
• Pernicious anaemia. Autoimmune destruction of gastric parietal cells produces atrophic gastric mucosa and reduced secretion of intrinsic factor. Vitamin B12 deficiency results from failure to absorb cobalamin in the terminal ileum.
• Malabsorption syndromes. Intestinal disease affecting the terminal ileum can interrupt the normal enterohepatic circulation of vitamin B12 and result in vitamin B12 deficiency. Malabsorption can also result from poor release of vitamin B12 from food as a consequence of impaired secretion of acid and pepsin by the stomach.
• Drugs. A number of drugs can reduce vitamin B12 absorption, including metformin, aminosalicylic acid, nicotine, phenytoin and large doses of vitamin C.
Table 30.2 Causes of vitamin B12 and folate deficiency
|
Deficiency |
Cause |
Abnormality |
|
Vitamin B12 |
Inadequate dietary intake |
Veganism |
|
Reduced vitamin B12 absorption |
Pernicious anaemia |
|
|
Drugs |
Nitrous oxide (prolonged exposure) |
|
|
Congenital defects |
Transcobalamin deficiency |
|
|
Folate |
Inadequate dietary intake |
Poor diet: elderly, malnourished, poverty, alcoholics |
|
Malabsorption syndromes |
Gluten-sensitive enteropathy |
|
|
Increased folate requirements |
Pregnancy |
|
|
Anti-folate drugs |
Long-term antiepileptic use (phenytoin, primidone and phenobarbital) |
Vitamin B12 deficiency can result in:
• Subclinical disease: mild anaemia without clinical symptoms or signs.
• Megaloblastic anaemia (macrocytic anaemia with oval macrocytes and hypersegmented neutrophils).
• Subacute combined degeneration of the brain, spinal cord and peripheral nerves.
• Abnormalities of epithelial tissue, particularly the alimentary tract, e.g. sore tongue and malabsorption.
Cobalamin deficiency is diagnosed by measuring total plasma vitamin B12 (normal 150–450 pmol/L); this includes holotranscobalamin and holohaptocorrin. Studies now indicate that measuring holotranscobalamin (normal level 33–91 ng/L), the active portion of vitamin B12, is more sensitive and specific for vitamin B12 deficiency. In vitamin B12 deficiency the serum folate may be elevated and red cell folate reduced due to disturbance of normal absorption and metabolism (Fig. 30.2). Methylmalonic acid levels may be elevated and are relatively specific for vitamin B12 deficiency whereas elevated homocysteine levels are not.
Fig. 30.2 Schematic diagram showing the link between vitamin B12 and folate metabolism.
Management of vitamin B12 deficiency and prophylactic administration
Vitamin B12 administration is indicated for the prevention and treatment of deficiency. Hydroxocobalamin is the preferred form of vitamin B12 for clinical use. In vitamin B12 deficiency, hydroxocobalamin should be given at a dose of 1 mg intramuscularly three times per week for 2 weeks (6 doses) to replenish body vitamin B12 stores. Maintenance therapy (1 mg every 3 months) is required if the underlying cause cannot be corrected, such as in pernicious anaemia which requires lifelong vitamin B12 therapy. After commencing therapy, there is rapid clinical improvement, there is a blood reticulocyte peak at 5–7 days, and the haemoglobin, red cell count and haematocrit rise after 1 week. The blood indices normalise within 2 months. Failure to respond implies an incorrect or incomplete diagnosis (e.g. additional haematinic deficiency). Stimulation of erythropoiesis may deplete iron and folate stores and these may require supplementation. Hypokalaemia may occur at the height of the erythrocyte response in severe cases due to uptake of potassium by the rapidly increasing erythrocyte mass. Oral potassium should be considered prior to initiating therapy with low or borderline plasma potassium levels. Reversal of neurological damage is slow, rarely marked, and inversely related to the extent and duration of neuropathy. Adverse effects are extremely rare. Both vitamin B12 and folic acid should be administered in megaloblastic anaemia while plasma levels are awaited. Prophylactic vitamin B12 (e.g. for vegans) should be administered at a dose of 1 mg every 3 months.
Contraindications to cobalamin
Vitamin B12 should not be administered for undiagnosed anaemia. Proper haematological and biochemical workup is essential in determining the cause prior to commencement of therapy. Even a single dose of vitamin B12 can interfere with the haematological picture for weeks and result in a delay in diagnosis and instigation of the correct therapy.
Folic acid (pteroylglutamic acid)
Folic acid4 is one of the B group vitamins and is widely distributed, particularly in green vegetables, fruits, yeast and liver. A normal adult diet contains approximately 400 μg of folic acid (one-third in monoglutamate and two-thirds polyglutamate form) and 100–200 μg is absorbed. Daily requirements are 50–100 μg. Folate polyglutamate is deconjugated to the monoglutamate form prior to absorption in the proximal jejunum. Within the plasma folate is present mainly as 5-methyl tetrahydrofolate. This enters the cell and is demethylated to tetrahydrofolate, a process that requires vitamin B12 (see Fig. 30.2). Total folate content of the body is 6–10 mg, stores which will last for only 3–4 months on a folate-deficient diet. Folate is required for amino acid and DNA synthesis and cell division.
Folic acid deficiency
Deficiency of folic acid causes megaloblastic anaemia as a result of impaired production of purines and pyrimidines, essential for DNA synthesis. The haematological features are indistinguishable from vitamin B12 deficiency. It is critical to determine which of these haematinics is deficient, as incorrect therapy can have severe ramifications; specifically, folic acid supplements may accelerate progression of subacute combined degeneration of the spinal cord due to vitamin B12 deficiency.
Case study
A 26-year-old woman has a routine blood count performed in the third trimester of pregnancy. She is noted to be anaemic with a Hb of 5.3 g/dL with a mean cell volume of 102 fL (normal 80–100), mildly leucopenic (3.2 × 109/L) and thrombocytopenic (87 × 109/L). The blood film shows oval macrocytes, megaloblastic nucleated red blood cells and hypersegmented neutrophils. Biochemical analyses show serum folate 2.2 μg/L (normal = 3–16), red cell folate 80 μg/L (normal > 250), vitamin B12 350 ng/L (normal = 200–900), mild hyperbilirubinaemia and a normal ferritin. A full dietary history shows the patient has a poor diet containing minimal folic acid. The patient is treated with oral folic acid (5 mg daily until the red cell folate has normalised) and given dietary advice.
The most common causes of folic acid deficiency are those listed in Table 30.2.
Specific clinical settings in which folate deficiency can occur deserve mention. In pregnancy daily folate requirements increase to 400 μg/day in the third trimester to meet the demands of the developing fetus and placenta. This increase is commonly not met by a normal Western diet. The problem is even greater in developing countries where nutritional deficiency may be aggravated by increased requirements due to haemoglobinopathies and endemic malaria. Premature neonates require folate supplementation because they lack the build-up of folate stores that normally occurs in the last weeks of pregnancy and hence are commonly deficient. In chronic haemolytic anaemia (e.g. autoimmune haemolytic anaemia; sickle cell anaemia; hereditary spherocytosis) the compensatory increased bone marrow erythroid activity results in increased folate demand. Renal dialysis removes folate and therefore chronic haemodialysis or peritoneal dialysis can result in folate depletion. A number of drugs interfere with folate absorption, inhibit the activity of folate dependent enzymes or displace folate from transport proteins. Dihydrofolate reductase is inhibited by methotrexate, trimethoprim and pyrimethamine. The antidote to these drugs is folinic acid (5-methyl tetrahydrofolate).
Management of folic acid deficiency and prophylactic administration
Large doses of synthetic folic acid (5 mg orally daily for 4 months) are used to treat folate deficiency irrespective of the cause; up to 15 mg may be required if there is malabsorption. Long-term use may be required if the underlying condition cannot be controlled and/or folate deficiency is likely to recur (e.g. sickle cell disease). It is critical that vitamin B12 deficiency be excluded and treated prior to commencement of folic acid therapy. If not, cobalamin neuropathy may develop. Adverse reactions are rare; allergy occurs, and status epilepticus may be precipitated. There is no advantage in giving folinic acid instead of folic acid, except in the treatment of the toxic effects of folic acid antagonists such as methotrexate.
In many countries foods such as flour are fortified to prevent neural tube defects. Assessment of folate status before conception should be considered and folate supplementation (400 μg/day orally) given if required. In women hoping to conceive who have had a previous neural tube defect fetus, 5 mg folate daily is recommended.5,6 Prophylactic folic acid (200–500 μg daily) should be taken throughout pregnancy; this is generally administered together with prophylactic iron.
Haemolytic anaemia
Haemolytic anaemia occurs where red cells survive less than 120 days and there is an inadequate bone marrow erythropoietic response. Acquired haemolytic anaemia may be due to immune (autoimmune, alloimmune or drug-induced) or non-immune (e.g. secondary to infection, mechanical trauma, drugs) causes. Inherited haemolytic anaemias may be due to defects of the red cell membrane (e.g. hereditary spherocytosis), abnormalities of red cell metabolism (e.g. glucose 6-phosphate dehydrogenase deficiency or pyruvate kinase deficiency) or defective globin chains (i.e. haemoglobinopathies). Management is determined by the underlying mechanism. In general, iron should not be given in haemolytic anaemia since iron from lysed cells is recirculated; moreover, in chronic haemolysis there is increased iron absorption and iron supplementation can result in haemosiderosis. Iron may be required in chronic intravascular haemolysis as haemoglobinuria may result in iron deficiency. Folate supplementation is commonly required with chronic haemolysis as the compensatory erythroid hyperplasia results in increased folic acid utilisation. Some of the more common types of haemolytic anaemia are described.
Autoimmune haemolytic anaemia
Autoimmune haemolytic anaemia (AIHA) occurs as a result of autoantibodies causing premature red cell destruction. AIHA may be idiopathic or secondary to malignancy (especially lymphoid neoplasms), drugs, infection and connective tissue diseases. The autoantibodies are described as ‘warm’ or ‘cold’, based on their thermal range of activity. Warm AIHA is caused by IgG antibodies and results in extravascular haemolysis by Fc receptor-mediated immune clearance; it is characterised by spherocytes on the blood film. Corticosteroids are used (typically prednisone 1–1.5 mg/kg daily) to reduce antibody production, suppress red cell clearance and down-regulate Fc receptors; the median time to response is 7–10 days. When there is evidence of a haematological response, the corticosteroid dose is gradually reduced to minimise complications of long-term use. A lack of response by 3 weeks prompts alternative therapy, such as high dose intravenous γ-globulin, other immunosuppressive therapies (e.g. vinca alkaloids, azathioprine and cyclophosphamide), danazol or rituximab (CD20 monoclonal antibody). Corticosteroids and alkylating agents are usually ineffective in cold AIHA. In both warm and cold AIHA, folate supplementation is commonly required (5 mg/day) to compensate for the demands from increased erythropoiesis.
Drug-induced haemolytic anaemia
Case study
A 32-year-old woman presented with severe lethargy and jaundice 10 days following caesarean section. She had received 1 g cefotetan as antibiotic prophylaxis prior to surgery. On presentation her Hb was 5.2 g/dL, she had spherocytes on her blood film, an unconjugated hyperbilirubinaemia, elevated lactate dehydrogenase and a positive direct antiglobulin test (IgG) with drug-associated antibodies. A diagnosis of life-threatening cephalosporin-induced haemolytic anaemia was made. Due to the severity of her anaemia she required red cell transfusion support. Folic acid (5 mg/day for 2 weeks) was administered. She made a spontaneous recovery.
Many drugs can cause increased red cell destruction by immune or non-immune mechanisms (Table 30.3). Drug-induced immune-mediated haemolytic anaemia is most commonly secondary to penicillins, second- and third-generation cephalosporins (in particular cefotetan and ceftriaxone), quinine, quinidine and α-methyldopa. Other drugs and toxins can cause direct damage to the red cell membrane (e.g. copper, mitomycin C) or induce oxidative haemolysis (e.g. sulfonamides, dapsone). Drug withdrawal is usually sufficient but, if severe, red cell transfusions may be required.
Table 30.3 Some drugs and chemicals that can cause haemolytic anaemia
|
Mechanism |
Drug, chemical or toxin |
|
Immune-mediated haemolytic anaemia |
Cephalosporins |
|
Oxidative haemolytic anaemia |
Aminosalicylic acid |
|
Direct red cell membrane damage |
Amphotericin |
Glucose-6-phosphate dehydrogenase deficiency
Case study
An 18-year-old male presented to a hospital emergency department febrile, dyspnoeic and jaundiced after eating a meal which included fava beans. He was anaemic with a Hb of 8.7 g/dL and the blood film showed ‘bite’ cells.7 A methyl violet stain for Heinz bodies was positive. Bilirubin and lactate dehydrogenase were elevated and his G6PD was reduced (20% activity). A diagnosis of G6PD-deficiency was made and classified as a ‘mild deficiency’. He was managed conservatively and did not require a transfusion. He was advised to avoid foods (broad beans) and drugs (i.e. primaquine, sulfonamides) that cause oxidative haemolysis, and to present early for medical attention at times of infections.
Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an X-linked inherited enzyme defect that causes haemolytic anaemia following an acute febrile illness, hypoxia or intake of drugs, foods or other substances that cause oxidation of haemoglobin (Table 30.4). Diagnosis is made on a blood film which shows ‘bite’ cells, resulting from splenic removal of oxidised haemoglobin, a positive Heinz body test and a G6PD enzyme assay. Treatment is supportive and avoidance of drugs and foods (e.g. fava beans) with oxidant potential.
Table 30.4 Drugs and substances that can cause oxidative haemolysis in G6PD deficiency
|
Drug type |
Drug name |
|
Analgesics |
Pyridium (phenazopyridine) |
|
Anti-bacterials |
Dapsone |
|
Anti-malarials |
Primaquine |
|
Sulphonamides and sulphones |
Sulphamethoxazole (including co-trimoxazole) |
|
Others |
Ascorbic acid |
Haemoglobinopathies
Sickle cell anaemia
In sickle cell disease, deoxygenated haemoglobin S (HbS) forms polymers resulting in erythrocytes becoming inflexible ‘sickle-shaped’ forms. Sickle red cells can obstruct blood flow and cause the clinical features of sickle cell disease, principally haemolytic anaemia, acute chest syndrome and painful crises. Hydroxycarbamide (hydroxyurea) can be used in sickle cell disease to increase the HbF levels in maturing erythrocytes, decrease HbS polymerisation and erythrocyte sickling, and reduce the frequency and severity of sickling complications. It also increases nitric oxide (promoting vasodilatation), causes a fall in leucocyte count and improves red cellular hydration, all of which result in a reduction in vaso-occlusive events.8 The indications for initiating hydroxycarbamide include frequent acute painful crises and acute chest syndrome. Beneficial effects of hydroxycarbamide have been seen in adults, children and infants, with a reduction in hospital admissions, pain, acute chest syndrome, blood transfusions and mortality. Neurological complications, e.g. stroke, may not be reduced. Long-term daily administration of hydroxycarbamide raises HbF levels to 15–20% (normally < 1% in adults). Hydroxycarbamide is relatively non-toxic, its myelosuppressive effects are reversible and the long-term risk of leukaemogenesis is negligible. There is no adverse effect on growth or development in children and it does not appear to increase the risk of malignancy.
Thalassaemia
Thalassaemias9 vary in their severity from clinically silent to transfusion-dependent with many being of intermediate severity. Severely affected thalassaemia major patients are likely to require regular red blood cell transfusions and iron chelation therapy (see p. 499). Iron chelation is usually started after 1 year of monthly blood transfusions. Patients are monitored regularly to assess growth, endocrine and cardiac function, iron status (serum ferritin, MRI for liver iron concentration) and adverse effects related to therapy. Patients with less severe thalassaemia (thalassaemia intermedia) generally only require intermittent transfusions; the need for iron chelation therapy is based on iron load (ferritin). Hydroxycarbamide can be used in these patients, in the same manner as for sickle cell disease, to increase HbF and total haemoglobin levels. Individuals with thalassaemia minor (i.e. carriers) are typically asymptomatic and do not require therapy.
Aplastic anaemia
Aplastic anaemia may be idiopathic or secondary to chemicals (e.g. benzene), drugs or infection. Treatment is determined by the severity of the cytopenias, patient age, availability of a marrow donor, and, less commonly, the cause. Therapeutic choice is between immunosuppression and allogeneic bone marrow transplantation. The latter carries survival rates of 75–80% but chronic graft-versus-host disease causes continued morbidity. Good supportive treatment is important (i.e. antibiotics and transfusions). Patients who are not candidates for transplantation due to age or lack of a donor (up to 70% of patients) receive immunosuppression. Anti-thymocyte globulin (ATG) induces haematological responses, transfusion independence and freedom from infection in 70% of patients. Addition of ciclosporin (5 mg/kg/day) to ATG improves the speed of response, with survival rates in responders up to 90%. Treatment should be initiated within 14 days of diagnosis and responses generally occur within 4 months. Adverse effects of ATG include fever, rigors and lethargy and these are common in the first 2 days of treatment. Approximately 7–10 days post-infusion serum sickness, with rash, joint pain and fever may occur; this can be modified by giving prednisolone (1 mg/kg/day). Anaphylaxis and exacerbation of the cytopenias are rare adverse effects. Relapse occurs in 35% within 5 years but relapsed patients may respond to further immunosuppression (rabbit antilymphocyte globulin after initial ATG). In refractory patients G-CSF (5–10 mg/kg subcutaneous) and ESA can improve the neutrophil count and haemoglobin, respectively.
Polycythaemia vera
Polycythaemia vera (PV) is a myeloproliferative neoplasm where there is uncontrolled over-production of erythrocytes in the bone marrow. The clinical manifestations include arterial (especially coronary and cerebral) and venous vascular events, splenic pain, pruritis, gout and constitutional symptoms such as fatigue. PV may progress to myelofibrosis or undergo leukaemic transformation to acute myeloid leukaemia (AML). The aims of treatment are to reduce the risk of thrombosis and haemorrhage, minimise the risk of transformation to myelofibrosis and AML and manage complications.
Management of PV
Venesection of 300–500 mL is performed weekly or twice weekly to achieve a haematocrit of less than 0.45, and thereafter every 3–6 months to maintain the haematocrit at this level. Iron deficiency may occur and requires cautious treatment. Low-dose aspirin (100 mg/day) reduces thrombotic complications. Cytoreductive therapy should be considered when venesection is poorly tolerated, there is symptomatic or progressive splenomegaly, thrombocytosis or the presence of symptoms that may indicate disease progression (e.g. night sweats; weight loss). Optimal therapy is determined by the patient's age and the adverse effects of each drug.
Hydroxycarbamide
(hydroxyurea) is the most commonly used drug in PV and is given orally. It inhibits ribonucleotide reductase, an enzyme which has a rate-limiting role in the regulation of DNA synthesis. Hydroxycarbamide (1–2 g/daily) inhibits myeloproliferation, normalises the platelet count and spleen size, reduces venesection requirements, reduces the incidence of thrombosis and ameliorates hypercatabolic symptoms. It is generally good at controlling PV but requires continuous use. Hydroxycarbamide is first-line therapy for patients over 40 years of age. Its use should be limited in younger patients due to the (low) risk of leukaemogenesis. Complications are leucopenia and thrombocytopenia.
Interferon-α
(IFN-α) is first-line therapy for PV in patients under the age of 40 years and second-line for patients aged 40–75 years. IFN-α suppresses the proliferation of haemopoietic progenitor cells in the marrow. It is effective in controlling the platelet count, haematocrit, splenomegaly and constitutional symptoms in PV and is not leukaemogenic; it may be used in pregnant women. Treatment is continuous at doses of 3–5 mU three times/week by subcutaneous injection. Unwanted effects include ’flu-like symptoms, fatigue and depression.
Anagrelide,
a prostaglandin synthetase inhibitor, inhibits cyclic nucleotide phosphodiesterase and the release of arachidonic acid from phospholipase. It is second-line therapy for patients up to the age of 75 years. Anagrelide lowers the platelet count by inhibiting megakaryocyte differentiation; it can control the thrombocytosis of venesection and can be used in combination with hydroxycarbamide. It is orally active and the usual dose is 1–2 mg daily. Adverse effects are related to its vasodilatory properties and include headache, palpitations and fluid retention.
Busulfan
is an alkylating agent that reduces vascular events and delays myelofibrosis in PV. Mutagenic potential restricts its use to older patients or when other treatments are poorly tolerated. The usual dose is 25–75 mg as a single dose administered every 2–3 months. Pipobroman is a bromide derivative of piperazine which inhibits DNA and RNA polymerase and reduces the incorporation of pyrimidine nucleotides into DNA. It is effective in long-term control of PV and has low leukaemogenic potential. Radioactive phosphorus (32P) is concentrated in bone and rapidly dividing cells; consequently erythroid precursors receive most of the β-irradiation. 32P can be used intermittently and is good at controlling PV. It increases the rate of leukaemic transformation and therefore use should be restricted to elderly patients.
Therapy of other clinical features of PV
Pruritis generally improves with reduction in the haematocrit. In some cases paroxetine and antihistamines (H1- and/or H2-histamine-receptor blockade) may be required. Hyperuricaemia, due to cell destruction, is corrected with allopurinol.
Haemopoietic growth factors
Haemopoietic growth factors, such as ESA and granulocyte colony-stimulating factor (G-CSF), are produced by recombinant DNA technology. These can be administered to stimulate erythroid and myeloid lineages in the bone marrow and are potentially useful for secondary anaemias (e.g. chronic renal failure) and neutropenia due to disease or chemotherapy.10
Erythropoiesis-stimulating agents
Erythropoietin (EPO), a glycoprotein hormone encoded by a gene on chromosome 7 (7q), controls and regulates erythropoiesis. The kidneys produce 90% and the liver the majority of the remainder. EPO binds to receptors on erythrocyte progenitors in the bone marrow and stimulates their proliferation, differentiation and survival. Normal EPO production increases with hypoxia and decreases with polycythaemia. The anaemia of chronic renal failure is largely due to failure of erythropoietin production.
Therapeutic EPO agents are classified as erythropoiesis-stimulating agents (ESA). Recombinant human erythropoietin (epoetin) can be given subcutaneously or intravenously and has a t½ of 4 h. The dose and frequency of administration is dependent on the indication and response. For optimal erythropoietic response there must be adequate iron and folate stores (as above). The maximum reticulocyte response is seen at 4 days. Epoetin-α and -β are two recombinant forms of EPO available for the treatment of EPO-responsive anaemia and these have equal clinical efficacy. Darbepoetin is a hyperglycosylated EPO-derivative with a longer t½ than epoetin. This allows less frequent administration, e.g. once weekly or even less frequently, for anaemia of renal failure and chemotherapy. There is no clinically significant difference between darbepoetin and epoetin in haemoglobin response, transfusion reduction or thromboembolic events.
Clinical uses of ESA
Anaemia of chronic renal failure
EPO is effective (50–150 units/kg) in chronic renal failure patients with symptoms attributable to anaemia and a Hb < 11 g/dL. The aim of EPO therapy is to restore the haemoglobin to 11–12 g/dL. Higher target Hb levels (≥ 13 g/L) are reported to result in risk of stroke, serious cardiovascular events and death. Even partial correction of renal failure-induced anaemia improves physiological and clinical status, enhances quality of life, increases survival and can result in transfusion independence. It is critical that plentiful iron is available and the serum ferritin should be maintained > 200 μg/L. Intravenous iron may be required to optimise iron stores prior to EPO administration. In patients with renal failure, a dose-dependent increase in arterial blood pressure follows the rise in red cell mass, and encephalopathy may occur in some hypertensive patients. Arteriovenous shunts of dialysis patients, especially those that are compromised, may thrombose because of increased blood viscosity.
Anaemia due to cancer chemotherapy
ESA have been used in the management of chemotherapy-induced anaemia (Hb < 10 g/dL).11 ESA administration can reduce the need for red cell transfusions, improve quality of life and reduce symptoms related to anaemia. There is clinical trial evidence that ESA administration increases tumour progression, tumour recurrence, serious cardiac and thrombotic events and death. These serious safety concerns have restricted the use of ESA in oncology.
Other clinical uses of EPO
In symptomatic chronic heart failure with mild anaemia (Hb < 10 g/dL) ESA treatment can reduce symptoms, and improve the anaemia and exercise tolerance. Epoetin has also been effective for anaemia of prematurity, rheumatoid arthritis myelodysplasia and HIV patients treated with zidovudine. In all of these settings higher doses of epoetin are required than in renal failure. EPO may be administered to reduce the need for blood transfusion in elective non-cardiac, non-vascular surgery, and can be considered before surgery for patients who decline blood transfusion.
Adverse effects of ESA. Venous thromboembolism is a well-recognised risk. Transient influenza-like symptoms may accompany initial intravenous injections of ESA. Pure red cell aplasia due to development of antibodies may occur after epoetin-α. As increased erythropoiesis outstrips iron and folate stores, iron and folate deficiency may develop, especially in dialysis patients. Prophylactic iron and folic acid therapy are therefore indicated.
Granulocyte colony-stimulating factor
Granulocyte colony-stimulating factor (G-CSF) is a glycoprotein cytokine that stimulates the growth, differentiation and activity of myeloid cells. Recombinant G-CSF, administered intravenously or subcutaneously (5–10 μg/kg per dose), has the following applications:
• Haemopoietic stem cell mobilisation into the peripheral blood for autologous or allogeneic transplantation. Blood mobilised progenitor cells are associated with earlier neutrophil and platelet recovery, fewer transfusions and shorter hospitalisation than those from bone marrow.
• To hasten neutrophil recovery following myelosuppressive chemotherapy, after autologous and allogeneic bone marrow transplantation, in aplastic anaemia and AIDS. G-CSF increases the neutrophil count four- to five-fold within hours of administration, shortens the duration of neutropenia and reduces infections in patients who have received cytotoxic myelosuppressive chemotherapy.
• To improve the neutrophil count in myelodysplastic syndromes, and congenital, cyclical and idiopathic neutropenia. G-CSF can reduce the risk of life-threatening infections and prolong survival.
G-CSF is rapidly cleared after intravenous injection (t½ 2 h). Pegfilgrastim, which has polyethylene glycol covalently bound to G-CSF, has a longer t½ (40 h) allowing for less frequent dosing, e.g. once per chemotherapy cycle. High concentrations of G-CSF are found in plasma, bone marrow and kidneys; it is degraded to amino acids and excreted in urine.
Adverse effects of G-CSF are medullary bone pain which occurs with high intravenous doses, musculoskeletal pain, dysuria, splenomegaly, allergic reactions and raised liver enzymes. If administered to patients with sickle cell anaemia it may precipitate painful crises. There is an increased risk of acute myeloid leukaemia with chronic G-CSF administration in children with congenital neutropenia.
Guide to further reading
Angelucci E., Barosi G., Camaschella C., et al. Italian Society of Haematology practice guidelines for the management of iron overload in thalassemia major and related disorders. Haematologica. 2008;93:741–752.
Bennett C.L., Silver S.M., Djulbegovic B., et al. Venous thromboembolism and mortality associated with recombinant erythropoietin and darbepoetin administration for the treatment of cancer-associated anaemia. J. Am. Med. Assoc.. 2008;299:914–924.
Bohlius J., Schmidlin K., Brillant C., et al. Erythropoietin or darbepoetin for patients with cancer – meta-analysis based on individual patient data. Cochrane Database Syst Rev. 8(3), 2009. CD007303
Carmel R. Current concepts in cobalamin deficiency. Annu. Rev. Med.. 2000;51:357–375.
Davies J.K., Guinan E.C. An update on the management of severe idiopathic aplastic anaemia in children. Br. J. Haematol.. 2007;136:549–556.
Fleming R.E., Bacon B.R. Orchestration of iron homeostasis. N. Engl. J. Med.. 2005;352:1741–1744.
Kaushansky K. Lineage-specific haematopoietic growth factors. N. Engl. J. Med.. 2006;354:2034–2045.
Lanzkron S., Strouse J.J., Wilson R., et al. Systematic review: hydroxyurea for the treatment of adults with sickle cell disease. Ann. Intern. Med.. 2008;148:939–955.
Lawler P.R., Filion K.B., Eisenberg M.J. Correcting anaemia heart failure: the efficacy and safety of erythropoiesis-stimulating agents. J. Card. Fail.. 2010;16:649–658.
McMullin M.F., Bareford D., Campbell P., et al. General Haematology Task Force of the British Committee for Standards in Haematology. Guidelines for the diagnosis, investigation and management of polycythaemia/erythrocytosis. Br. J. Haematol.. 2005;130:174–195.
Marsh J.C., Ball S.E., Cavenagh J., et al. Guidelines for the diagnosis and management of aplastic anaemia. British Committee for Standards in Haematology. Br. J. Haematol.. 2009;147:43–70.
Mehta A., Mason P.J., Vulliamy T.J. Glucose-6-phosphate dehydrogenase deficiency. Baillieres Best Pract. Res. Clin. Haematol.. 2000;13:21–38.
Ngo K., Kotecha D., Walters J.A. Erythropoiesis-stimulating agents for anaemia in chronic heart failure. Cochrane Database Syst. Rev. 8(3), 2009. CD007613
Rund D., Rachmilewitz E. β-Thalassemia. N. Engl. J. Med.. 2005;353:1135–1146.
Scheinberg P., Wu C.O., Nunez O., et al. Predicting response to immunosuppressive therapy and survival in severe aplastic anaemia. Br. J. Haematol.. 2009;144:206–216.
Vichinsky E. Clinical application of deferasirox: practical patient management. Am. J. Hematol.. 2008;83:398–402.
Wickramasinghe S.N. Diagnosis of megaloblastic anaemias. Blood Rev.. 2006;20:299–318.
1 Staining can be minimised by inserting the needle through the skin and then moving the subcutaneous tissue laterally before entering muscle, so that the needle track is disrupted when the needle is withdrawn (Z technique).
2 A 26-year-old subject with β-thalassaemia major had been transfused with 404 units of blood over his lifetime. His iron stores were so high (estimated at above 100 g) that he triggered a metal detector at an airport security checkpoint (Jim R T S 1979 Lancet ii:1028 [letter]).
3 Tenenbein M, Kowalski S, Sienko A et al 1992 Lancet 339:699–701.
4 Latin: folium, a leaf.
5 Hernández-Díaz S et al 1991 Lancet 338:131–137.
6 A supplement of folic acid 5 mg/day is proposed for fuller risk reduction (Wald N J, Law M R, Morris J K, Walk D S 2001 Quantifying the effect of folic acid. Lancet 358:2069–2073).
7 The profile of some red cells carries a concave defect (like a bite), an appearance that is indicative of haemolytic anaemia.
8 Steinberg M H, Barton F, Castro O et al 2003 Effect of hydroxyurea on mortality and morbidity in adult sickle cell anaemia: risks and benefits up to 9 years of treatment. Journal of the American Medical Association 289:1645–1651.
9 The genetic defect results in reduced rate of synthesis or absent synthesis of one of the globin chains that make up haemoglobin.
10 Ozer H, Armitage J O, Bennett C L 2000 Update of recommendations for the use of haematopoietic colony-stimulating factors: evidence-based, clinical practice guidelines. Journal of Clinical Oncology 18:3558–3585.
11 Rizzo J D, Lichtin A E, Woolf S H et al 2002 Use of epoetin in patients with cancer: evidence-based clinical practice guidelines of the American Society of Clinical Oncology and the American Society of Haematology. Blood 100:2303–2320.