Reduced proliferation of precursors	Defective maturation of precursors
Iron deficiency	Vitamin B₁₂ deficiency
Anaemia of chronic disease	Folate deficiency
Anaemia of renal failure	Iron deficiency
Aplastic anaemia (primary)	Disorders of
Aplastic anaemia (secondary to drugs, etc.)	– globin synthesis (thalassaemias) – iron metabolism (e.g. sideroblastic)

Infiltration of the bone marrow:

– leukaemia or lymphoma

– myelofibrosis

– metastases

Myelodysplastic syndrome

This chapter will cover some of the more common anaemias that involve drug therapy:

Microcytic anaemias	iron deficiency anaemia
	anaemia of chronic disease
	sideroblastic anaemia
Megaloblastic anaemias	folate deficiency
Megaloblastic anaemias	vitamin B₁₂ deficiency
Haemolytic anaemias	autoimmune haemolytic anaemia
	sickle cell disease
	thalassaemia
	glucose-6-phosphate dehydrogenase deficiency

Normal erythropoiesis

It is thought that white cells, red cells and platelets are all derived from a common cell known as the pluripotent stem cell found in the bone marrow. As these cells mature, they become committed to a specific cell line (Fig. 49.1). The red cells mature through the various stages, during which time they synthesise haemoglobin, DNA and RNA. Reticulocytes are found in the peripheral circulation for 24 h before maturing into erythrocytes. Reticulocytes are released into the peripheral circulation prematurely during times of increased erythropoiesis.

Fig. 49.1 Simplified diagram of some of the stages within erythropoiesis.

Erythropoietin is a hormone produced by the cells of the renal cortex. The kidney responds to hypoxia and anaemia by increasing the production of erythropoietin. The red cell progenitors BFU-E and CFU-E have receptors on their surface. When erythropoietin binds to these receptors, it promotes differentiation and division, and consequently increased erythropoiesis. Patients with end-stage renal disease fail to produce appropriate amounts of erthropoietin and so develop anaemia. Erythropoietin production is also impaired in other conditions such as rheumatoid arthritis, cancer and sickle cell disease, though the impairment is not as great as in renal disease. Also of interest is the fact that theophylline decreases erythropoietin production, though the clinical relevance of this is uncertain.

Each day approximately 2 × 10¹¹ erythrocytes enter the circulation. Normal erythrocytes survive in the peripheral circulation for about 120 days. Abnormal erythrocytes have a shortened lifespan. At the end of their life, the red cells are destroyed by the cells of the reticuloendothelial system found in the spleen and bone marrow. Iron is removed from the haem component of haemoglobin and transported back to the bone marrow for reuse. The pyrole ring from globin is excreted as conjugated bilirubin by the liver, and the polypeptide portion enters the body’s protein pool.

Clinical manifestations

In its mildest form anaemia results in tiredness and lethargy; at its most severe it results in death unless treated. There is some suggestion that even mild anaemia may inhibit physical exercise and result in reduced mental performance. The reduced oxygen-carrying capacity of the blood leads to reduced tissue oxygenation and widespread organ dysfunction (Box 49.1).

A rapid blood loss, for example, haemorrhage, produces shock, with collapse, dyspnoea and tachycardia. Anaemia that develops over a period of time allows the body to partially compensate. As the anaemia becomes worse, more and more signs and symptoms may develop.

Even though in anaemia the amount of haemoglobin is reduced, all the blood that passes through the lungs is fully oxygenated. Increasing the respiratory rate or increasing the FiO₂ (fraction of inspired oxygen) will not improve tissue oxygenation. When the haemoglobin falls below 7 or 8 g/dL, there is almost always a compensatory increase in cardiac output.

Investigations

It is essential to find the cause of the anaemia; there is no place for ‘blind’ treatment. In most patients, the anaemia is a consequence of a reduced concentration of haemoglobin in each red cell and/or a reduced number of red cells in the peripheral circulation. Blood volumes may be increased in pregnancy and heart failure and haemoglobin concentration appear falsely low. Splenomegaly and signs of heart failure are sure signs of an increased blood volume. A blood transfusion in such a patient would precipitate left ventricular failure.

The most important parameter to assess anaemia is the haemoglobin concentration of the blood. It is also usual to count the number of red cells. In addition the size, shape and colour all contribute to the investigation (Box 49.2). The mean corpuscular volume (MCV) is a useful parameter that helps determine the type of the anaemia. However, care must be taken since the MCV indicates the average size of the cells. If there are two pathologies, where one causes large cells and other causes small cells, the MCV may appear normal or be misleading. Following on from this baseline other investigations may be required. Bone marrow examination by either aspiration or trephine may be needed to make a diagnosis.

Iron deficiency anaemia

Epidemiology

Iron deficiency anaemia is the commonest form of anaemia worldwide and may be present in up to 20% of the world’s population. A diet deficient in iron, parasitic infestations, for example, hookworm (causing blood loss), and multiple pregnancies contribute to its high prevalence in underdeveloped countries. Even in Western societies, it has been reported that as many as 20% of menstruating females show a rise in haemoglobin levels on iron therapy.

Pathophysiology

The elimination of iron is not controlled physiologically, so the homeostasis is maintained by controlling iron absorption. Iron is absorbed mainly from the duodenum and jejunum. Absorption itself is inefficient; iron bound to haem (found in red meat) is better absorbed than iron found in green vegetables. The presence of phosphates and phytates in some vegetables leads to the formation of unabsorbable iron complexes, whilst ascorbic acid increases the absorption of iron. In a healthy adult, approximately 10% of the dietary iron intake will be absorbed. Iron is transported around the body bound to a serum protein called transferrin. Normally, this protein is only one-third saturated with iron.

Anaemia may result from a mismatch between the body’s iron requirements and iron absorption. The demand for iron varies with age (Table 49.2). Diets deficient in animal protein or ascorbic acid may not provide sufficient available iron to meet the demand. Poor nutrition in children in inner cities in the UK frequently leads to anaemia. Milk fortified with iron given to inner city infants up to the age of 18 months has been shown to increase haemoglobin levels and improve developmental performance compared to unmodified cow’s milk (Williams et al., 1999). A systematic review showed that iron supplementation in children over seven improved intelligence tests scores in those who were initially anaemic (Sachdev et al., 2005). However, universal iron supplementation may not be appropriate because there is a theoretic increased risk of susceptibility to infectious diseases, although this has only been demonstrated for diarrhoea (Gera and Sachdev, 2002) and malaria in endemic areas (Prentice et al., 2007). Targeting supplementation only to children with anaemia and withholding iron supplementation during malaria treatment is sensible as iron may inhibit treatment, and absorption of oral iron is blocked by the inflammatory response.

Table 49.2 Typical daily requirements of iron

Infant (0–4 months)	0.5 mg
Adolescent male	1.8 mg
Adolescent female	2.4 mg
Adult male	0.9 mg
Menstruating female	2.0 mg
In pregnancy	3–5 mg
Postmenopausal female	0.9 mg

Malabsorption of iron has been reported in patients with coeliac disease and in 50% of patients following partial gastrectomy. Tetracyclines, penicillamine and fluoroquinolines bind iron in the gastro-intestinal tract and reduce the absorption of iron from supplements. They probably do not affect the absorption of dietary iron.

During pregnancy, there is an increase in red cell mass but there is also a proportionally bigger increase in plasma volume, which results in a physiological dilutional anaemia. It is thought that the gut increases its ability to absorb iron during pregnancy to meet the additional demands of fetal red cell production. Some of the increased demand is met by the stopping of menstruation. If, however, there is inadequate iron absorption, then anaemia may result.

Clinical manifestations

In addition to the general symptoms of anaemia, various other features may be present (Box 49.4). The colour of the skin is very subjective and often unreliable. Patients at risk of heart failure may present with breathlessness when anaemic. Koilonychia, dysphagia and pica are found only after chronic iron deficiency and are relatively rare.

Box 49.4 Features of iron deficiency anaemia

Pale skin and mucous membranes

Painless glossitis

Angular stomatitis

Koilonychia (spoon shaped nails)

Dysphagia (due to pharyngeal web)

Pica (unusual cravings)

Atrophic gastritis

A full blood count is an essential screening test. The cells of the peripheral blood are microcytic and hypochromic with poikilocytes (often pencil shaped) and occasional target cells (abnormal thin erythrocytes which when stained show a dark centre and peripheral ring).

The main parameter used to help establish the iron status of the patient is the serum ferritin. The serum ferritin level is low in iron deficiency anaemia and markedly raised in iron overload. It is a good measure of the iron stores in the body. Care needs to be used in interpreting raised ferritin levels as these are sometimes found in cancer, inflammatory conditions and liver disease. Serum iron is a less useful parameter and exhibits diurnal variation, being higher in the morning.

Investigations

The aim of treatment is to correct the anaemia and replenish iron stores. Although the treatment of iron deficiency anaemia is relatively simple, it should not be embarked upon lightly. It is important to resolve the underlying cause as far as possible. Since gastro-intestinal blood loss is the most common cause in men and postmenopausal women, examination of the upper and lower tract is an important investigation. If necessary, this may need to include upper gastro-intestinal tract endoscopy, colonoscopy, barium enema and small bowel biopsy.

Over-the-counter sales of iron should be discouraged except in those patients who have been fully investigated. It is not unknown for patients to be given iron unnecessarily, resulting in iron overload. Also, giving iron therapy to a patient who is continuing to bleed from their gastro-intestinal tract will not help resolve the underlying problem.

Treatment

Prophylaxis of iron deficiency anaemia was widely used in pregnancy (together with folic acid); however, it is now only used for women who have additional risk factors for iron deficiency, for example poor diet. Prophylaxis may also be used in menorrhagia, after partial gastrectomy and in some low birth weight infants, for example, premature twins.

If gastro-intestinal investigation has been performed and any underlying cause treated, all patients should receive iron supplementation to correct their anaemia and replenish stores. Oral iron in the ferrous form is cheap, safe and effective in most patients. Depending on the state of the body’s iron stores, it may be necessary to continue treatment for up to 6 months to both correct the anaemia and replenish body stores. The standard treatment is ferrous sulphate 200 mg two to three times a day. It typically takes between 1 and 2 weeks for the haemoglobin level to rise 1 g/dL. An earlier indication of the patient’s response can be seen by looking at the reticulocyte count, which should start to rise 2–3 days after starting effective treatment. Nausea or abdominal pains trouble some patients and this tends to be related to the dose of elemental iron. Giving the iron with food makes it better tolerated but tends to reduce the amount absorbed. Alternative salts of iron are sometimes tried; these tend to have fewer side effects simply because they contain less elemental iron (Table 49.3). Taking fewer ferrous sulphate tablets each day would have the same effect. A change in bowel habit (either constipation or diarrhoea) is sometimes reported, and this is probably not dose related. During the early stages of treatment, the body absorbs oral doses of iron better. Absorption is commonly around 15% of intake for the first 2–3 weeks but falls off to an average of 5% thereafter. It has been shown that for some patients eradication of Helicobacter pylori aids recovery from iron deficiency anaemia (Annibale et al., 1999).

Table 49.3 Elemental iron content of common oral preparations

Preparation	Approximate iron content (mg)
Tablets
Ferrous sulphate 210 mg	68
Ferrous gluconate 300 mg	35
Ferrous fumarate 322 mg	100
Ferrous fumarate 210 mg	68
Oral liquids
Ferrous fumarate 140 mg in 5 mL	45
Ferrous sulphate 125 mg in 1 mL	25
Sodium feredetate 190 mg in 5 mL	27.5

There are a number of modified-release oral preparations available. They have no clear therapeutic advantage over ferrous sulphate and are not recommended. Indeed, the modified-release characteristic may cause the oral iron to be carried into the lower gut, which is much poorer at absorbing iron than the duodenum. Modified-release preparations may be more likely to exacerbate diarrhoea in patients with inflammatory bowel disease or diverticulae.

There is a limited place for parenteral iron in iron deficiency anaemia; it should be reserved for patients who fail on oral therapy, usually because of poor adherence or intolerable gastro-intestinal side effects. For most patients when equivalent doses of oral and parenteral iron are used, there is no difference in the rate of at which the haemoglobin level rises. Patients who have lost blood acutely may require blood transfusions. The need for a rapid rise in haemoglobin is not an indication for parenteral iron. Intravenous iron has been shown to have some benefit during the perioperative management of anaemia in selected patients undergoing orthopaedic surgery, but not been observed in other types of surgery (Beris et al., 2008).

There is a risk of anaphylactoid reactions with intravenous iron but the incidence appears to be lower with the newer products than with the older preparations which have now been discontinued. Patients given the newer licensed products, iron dextran (CosmoFer®), iron sucrose (Venofer®), iron III isomaltoside (Monofer®) and ferric carboxymaltose (Ferinject®) should have a test dose, and there should be facilities for cardiopulmonary resuscitation available. The dose for all products is calculated from the body weight and iron deficit. The manufacturer’s product information provides details on administration. Some products can be given as a bolus injection (small doses) or by a short intravenous infusion or by a total dose infusion method. There seems to be a higher incidence of adverse reactions with the total dose infusions. Iron dextran may also be given by deep intramuscular injection. Intravenous iron should not be given during acute bacterial infections, since it may stimulate bacterial growth. As intravenous iron significantly reduces the oral absorption of iron, there is no rationale for giving oral iron for several days after administering intravenous iron.

Patient care

It is usual practice to advise patients to take iron products with or after meals as this probably reduces the incidence of nausea. Patients should be told that their faeces may become darker and that this is nothing to worry about. This is important in patients who have had malaena since they may associate their dark stools with the bleed and worry that they are still bleeding from the gastro-intestinal tract. The length of treatment, and adherence should be discussed and an explanation given that iron stores need to be replenished and that this takes time.

Anaemia of chronic disease

Epidemiology

This is the second most common form of anaemia (after iron deficiency). It is associated with a wide variety of inflammatory diseases including arthritis, malignancies, inflammatory bowel disease, HIV and other infections. It is increasingly being referred to as ‘anaemia of inflammation’. Related to anaemia of inflammation are the anaemias associated with chronic kidney disease and chronic heart failure.

Aetiology

In anaemia of inflammation, there appears to be impaired response to erythropoietin and the inflammatory cytokines lead to a reduction in the availability of circulating iron. This cytokine-mediated shift of iron from the circulation into reticuloendothelial system leads to iron restricted erythropoiesis, despite normal iron stores. In malignancies, in addition to the anaemia of inflammation, the cytotoxic treatments themselves decrease erythrocyte production through their anti-proliferative effects on the bone marrow. Certain cytotoxic agents, such as platinum-based therapies, are more likely to cause anaemia.

In chronic kidney disease and chronic heart failure, the reduced renal blood flow leads to a decreased production of erythropoietin.

Pathophysiology

During infections, inflammation and cancer, the inflammatory cytokines, in particular interleukin-6 released from macrophages, lead to an increased production of hepcidin. Hepcidin, a peptide produced by hepatocytes, plays a key role in iron availability. The hepcidin causes

• increased uptake of iron by hepatocytes;

• reduced iron absorption;

• reduced release of iron from macrophages.

The reduction of circulating iron is thought to limit this essential nutrient’s availability to invading microbes and tumour cells, blocking their proliferation.

In addition, the inflammatory cytokines increase the production of white blood cells which potentially lead to fewer stem cells being available for red cell production.

Clinical manifestations

Patients have the general symptoms of anaemia in addition to their symptoms of the chronic inflammatory condition. The anaemia frequently leads to a reduced quality of life for these patients.

Investigation

Patients have a hypochromic microcytic anaemia similar to iron deficiency anaemia, but the two conditions can be differentiated by reviewing other serum factors (see Table 49.4).

Table 49.4 Differentiation between iron deficiency anaemia and anaemia of chronic disease

Test	Iron deficiency anaemia	Anaemia of chronic disease
Serum iron	Low	Low
Serum ferritin	Low	Normal or high
Serum transferrin	High	Normal or low
Total iron binding capacity	High	Low

Treatment

Treating the underlying chronic condition is important. Blood transfusions are rarely needed in anaemia of inflammation. Oral iron therapy is not usually indicated despite the apparent reduced iron availability since these patients have a functional iron deficiency rather than an actual iron deficiency; also, the raised hepcidin levels reduce the oral absorption of iron.

A number of patients with chronic renal failure appear to have a functional iron deficiency that responds to intravenous iron. These patients, despite receiving oral iron and erythropoietin analogues, do respond with a rise in haemoglobin when given regular intravenous iron together with an erythropoietin analogue (Silverberg et al., 1996). Intravenous iron in combination with erythropoietin analogues is widely used in chronic kidney disease. The patient’s serum ferritin is monitored to check for iron overload. Concerns have been expressed about the possible long-term complications of intravenous iron, for example, atherosclerosis or increased risk of infection (Cavill, 2003). There appears to be a slightly increased risk of infections, but the improvement in anaemia leads to an improved quality of life.

Patients with anaemia-associated inflammatory bowel disease or with rheumatoid arthritis respond to intravenous iron; however, the use of intravenous iron in chronic inflammatory conditions is not generally recommended because of an increased risk of infections and also possible increased risk of acute cardiovascular events. Some small studies have shown intravenous iron to be beneficial in patients with heart failure, but currently this should be reserved for patients with proven iron deficiency and failure on oral iron (Dec, 2009).

Some patients with chronic disorders respond to erythropoietin analogues, none are licensed for use in chronic disease states other than anaemia associated with chronic renal failure or cancer. Elevated endogenous erythropoietin levels in patients with heart failure are associated with adverse outcomes (Felker, 2010). Some clinical trial data show a higher mortality and increased risk of tumour progression in patients with anaemia associated with cancer who have been treated with erythropoietins. It is not recommended that erythropoietin analogues are routinely used in the management of cancer treatment-induced anaemia (NICE, 2008). However, they may be considered, in combination with intravenous iron, for:

• women receiving platinum-based chemotherapy for ovarian cancer who have symptomatic anaemia with a haemoglobin concentration of 8 g/100 mL or lower. The use of erythropoietin analogues does not preclude the use of existing approaches to the management of anaemia, including blood transfusion when necessary;

• patients who cannot be given blood transfusions and who have profound cancer treatment-related anaemia that is likely to have an impact on survival.

Tocilizumab, the interleukin-6 antagonist monoclonal antibody licensed for use in rheumatoid arthritis, has been shown to improve haemoglobin levels (Raj, 2009). It has also been suggested that drugs which downregulate interleukin-6 may have some effect (Altschuler and Kast, 2005). Olanzepine and quetiapine (potent H₁ antagonists) are known to be regulators of interleukin-6 but are not used clinically for this purpose. Furthermore, it is not known what the other effects of modifying interleukin-6 or hepcidin would have on the chronic inflammatory condition.

Patient care

Some patients hearing they have anaemia may be tempted to go and purchase iron or other supplements. Careful explanation will help them make an informed decision.

Sideroblastic anaemias

Epidemiology

Sideroblastic anaemias are a group of conditions that are diagnosed by finding ring sideroblasts in the bone marrow. There are both hereditary and acquired forms. The hereditary forms are rare, whilst some of the acquired forms are relatively common with as many as 30% of alcoholics admitted to hospital having sideroblastic anaemia.

Aetiology

In the majority of hereditary forms, there is an X chromosome-linked pattern of inheritance. Both autosomal dominant and autosomal recessive families have been described. The main defect is a reduced activity of the enzyme 5-aminolevulinate synthase (ALAS) which is involved in haem synthesis.

The acquired forms include idiopathic forms, forms associated with myeloproliferative disorders and forms secondary to the ingestion of drugs (Box 49.5). Regardless of the cause, there is impaired haem synthesis, where the body has adequate iron stores but is unable to incorporate it into haemoglobin.

Pathophysiology

An examination of the bone marrow typically shows a number of erythroblasts that have iron granules surrounding the cell nucleus. These cells are known as ring sideroblasts. In the hereditary forms, there are low levels of ALAS. This mitochondrial enzyme is involved in the first step in the synthesis of haem and requires pyridoxal phosphate as a co-factor. Pyridoxine is a precursor for pyridoxal.

Drugs and toxins

Alcohol can lead to the formation of ring sideroblasts. Ethanol is metabolised to acetaldehyde. It is the acetaldehyde that lowers the levels of ALAS and pyridoxal. Isoniazid is a known cause of sideroblasts. In slow acetylators of isoniazid, the drug reacts with pyridoxal and the resulting product is then rapidly excreted. Pyridoxine prophylaxis is usually given to all patients on isoniazid. Doses of chloramphenicol over 2 g a day invariably lead to sideroblasts. This is thought to be due to the inhibition of mitochondrial protein synthesis. Sideroblastic anaemia is also associated with copper deficiency which can be caused by an overdose of the chelators: penicillamine, trientine and the experimental tetrathiomolybdate. These are all used in the treatment of Wilson’s disease.

Clinical manifestations

The hereditary forms typically develop in infancy or childhood. The anaemia can be severe or mild (haemoglobin typically 4–10 g/dL). There may be splenomegaly, which can lead to mild thrombocytopenia. The idiopathic acquired forms tend to develop insidiously usually in middle age or later. Many patients may be asymptomatic for long periods. In the forms associated with other disorders, the clinical picture tends to be dominated by the underlying diseases.

Investigations

The common finding in all forms is the presence of sideroblasts in the bone marrow. In the hereditary form, the red cells in the peripheral blood are hypochromic and microcytic. Despite this, there are frequently increased iron stores in the bone marrow. The serum iron and ferritin may also be high. In the acquired forms, the peripheral blood has hypochromic cells, which may be either normocytic or macrocytic.

Treatment

In patients with the hereditary forms, large doses of pyridoxine (typically 100–200 mg daily or even up to 400 mg) may reduce the severity of the anaemia. Long-term high-dose pyridoxine has been associated with peripheral neuropathy and so lower maintenance doses are sometimes tried. There have been case reports of patients responding to parenteral pyridoxal-5-phosphate after failing to respond to pyridoxine. Patients with an acquired form occasionally respond to high-dose pyridoxine, and a 2- to 3- month trial may be helpful in symptomatic patients. The response tends to be slow and only partial. Haem arginate (licensed for use in porphyria) has been shown to increase the red cell count and decrease the number of ring sideroblasts in some patients with acquired sideroblastic anaemia, in common with other conditions where an increased turnover of cells in the bone marrow and folate supplements are often necessary.

Although the peripheral blood cells are frequently hypochromic and microcytic, the condition is associated with increased iron stores; therefore, iron supplements should be avoided. The drugs and toxins (Box 49.5) tend to cause a reversible anaemia. Removing the offending agent usually resolves the anaemia.

Iron overload

Inevitably, some patients fail to respond to these treatments and frequent blood transfusions are required. This leads to the complications of iron overload and sensitisation and the risk of blood-borne virus transmission. The chelating agent desferrioxamine is given either by intravenous or by subcutaneous infusion. It binds free iron and iron bound to ferritin. Therapy should be considered when the serum ferritin level reaches 1000 μcg/L. Patients with very high ferritin levels may need daily infusions. Daily subcutaneous infusions using a disposable infusor or small infusion pump are suitable for home use. In the UK, a number of commercial healthcare companies provide a desferioxamine home care service. Published evidence suggests that for an equivalent dose, a longer infusion time results in increased iron excretion. Intravenous infusions can be given whenever the patient comes into hospital for a blood transfusion. Small doses (<200 mg) of vitamin C increase the effectiveness of desferrioxamine probably by facilitating iron release from the reticuloendothelial system. Higher doses of vitamin C are reported to increase the cardiotoxicity of iron overload. Patients with cardiac failure should not be given vitamin C with desferrioxamine. Desferrioxamine should not be given concurrently with prochlorperazine as prolonged unconsciousness may result.

There are two oral agents (desferiprone and deferasirox) licensed for iron overload. Deferiprone unfortunately causes reversible neutropenia in some patients and weekly neutrophil counts are required. It is licensed for patients intolerant of desferrioxamine. Deferasirox has been more recently introduced and comes as a dispersible tablet that needs to be taken at least 30 min before food. It is associated with a high incidence of gastro-intestinal ulcers and renal impairment. Decreased hearing and lens opacities have been reported. Auditory and ophthalmic testing is recommended before the start of treatment and at regular intervals thereafter (every 12 months).

Patient care

Few patients with hereditary or the idiopathic acquired forms have completely reversible anaemia. Patients need to be aware that treatment with pyridoxine may take several months before any signs of improvement are seen. They should be advised not to purchase over-the-counter iron or vitamin supplements, particularly ascorbic acid or pyridoxine, without discussing it with their consultant.

Megaloblastic anaemias

The megaloblastic anaemias are macrocytic anaemias (raised MCV). There is an abnormality in the maturation of haematopoietic cells in the bone marrow. In addition to abnormal red cells, the white cells and platelets may be affected. The two major causes are folate deficiency and vitamin B₁₂ deficiency. Pernicious anaemia is a specific autoimmune disease that causes malabsorption of vitamin B₁₂ due to a lack of intrinsic factor.

Epidemiology

Aetiology

Folate deficiency anaemia

Folate is readily available in a normal diet. Fruit, green vegetables and yeast all contain relatively large amounts of folate. Despite this relative abundance of folate in many foods, dietary deficiency is common, either as the sole cause of the folic acid deficiency anaemia or in conjunction with increased folate utilisation.

Vitamin B₁₂ deficiency anaemia

Deficiency occurs from inadequate intake or malabsorption. The only dietary source of vitamin B₁₂ (cyanocobalamin) is from food of animal origin. It is present in meat, fish, eggs, cheese and milk. Cooking does not usually destroy vitamin B₁₂. Daily requirements are between 1 and 3 μcg. Deficiency arises either from inadequate intake over a prolonged period or more commonly, in the West, from impaired absorption due to lack of intrinsic factor.

Malabsorption occurs if the distal ileum is removed; it may also occur with certain intestinal pathologies, particularly stagnant loop syndrome, tropical sprue and fish tapeworm infestation. Passive absorption does take place in the jejunum, but this is very inefficient and usually accounts for less than 1% of an oral dose.

Pathophysiology

The common biochemical defect in all megaloblastic anaemias is the inhibition of DNA synthesis in maturing cells.

Folate deficiency anaemia

The folate found in food is mainly conjugated to polyglutamic acid. Enzymes found in the gut convert the polyglutamate form to monoglutamate, which is readily absorbed. During absorption, the folate is methylated and reduced to methyltetrahydrofolate monoglutamate. This travels through the plasma and is transported into cells via a carrier specific for the tetrahydrofolate form. Within the cell, the methyl group is removed (in a reaction requiring vitamin B₁₂) and the folate is reconverted back to a polyglutamate form (Fig. 49.2). It has been suggested that the polyglutamate form prevents the folate leaking out of cells. The folate eventually acts as a coenzyme involved in a number of reactions including DNA and RNA synthesis. Defective DNA synthesis mainly affects cells with a rapid turnover, for example, gastro-intestinal cells and red blood cells, hence the sore tongue and anaemia seen in folate deficiency. During DNA synthesis, the folate coenzyme is oxidised to the dihydrofolate form, which is inactive and has to be reactivated by the enzyme dihydrofolate reductase. This is the enzyme inhibited by methotrexate and to a lesser extent by trimethoprim and pyrimethamine. Co-trimoxazole has been shown to increase the severity of megaloblastic anaemia.

Fig. 49.2 Simplified pathway of folate metabolism: (a) vitamin B₁₂ is required as a coenzyme for this reaction: (b) the enzyme dihydrofolate reductase converts inactive dihydrofolate back to the active tetrahydrofolate.

Vitamin B₁₂ deficiency

Absorption of vitamin B₁₂ is mainly by an active process. Enzymes in the stomach release vitamin B₁₂ from protein complexes. One molecule of vitamin B₁₂ then combines with one molecule of a glycoprotein called intrinsic factor. The intrinsic factor protects the vitamin B₁₂ from breakdown by microorganisms. There are specific receptors in the distal ileum for the intrinsic factor-vitamin B₁₂ complex. The vitamin B₁₂ enters the ileal cell and is then transported through the blood attached to transport proteins. Intrinsic factor does not appear in the blood.

Since intrinsic factor is only produced by the gastric parietal cells, a total gastrectomy always leads to vitamin B₁₂ deficiency. Approximately 10–15% of patients who have had a partial gastrectomy also develop deficiency. The onset of anaemia is usually delayed because the body typically has stores of 2–3 mg, which is sufficient for 2–3 years. Vitamin B₁₂ is a coenzyme for the removal of a methyl group from methyltetrahydrofolate. Lack of vitamin B₁₂ traps the folate as methyltetrahydrofolate and prevents DNA synthesis (Fig. 49.2). The exact mechanism by which vitamin B₁₂ deficiency causes neuropathy is not clear but may be due to a defect in the methylation reactions needed for myelin formation.

Pernicious anaemia

Pernicious anaemia is probably autoimmune in origin. Patients typically have a gastric atrophy and no (or virtually no) intrinsic factor secretion. Although not present in all patients, two different antibodies have been found in the serum of some patients with pernicious anaemia.

Clinical manifestations

In addition to the general features of anaemia, megaloblastic anaemia, of which folic acid deficiency and B₁₂ deficiency anaemia are the two most common examples, has certain characteristics described in Box 49.6.

Folate deficiency anaemia

Alcoholics and the elderly are particularly prone to nutritional deficiency. Elderly people living alone on tea and toast are typical examples of patients at risk. Many alcoholics develop deficiency due to their poor diet; although some beers contain small amounts of folate, spirits contain none. A number of drugs have been implicated in causing folate deficiency (Box 49.7). Actual megaloblastic anaemia from drug therapy is uncommon, and the exact mechanism(s) has not always been established. Serious malabsorption can occur in tropical sprue and coeliac disease. Reduced absorption is seen in Crohn’s disease and following partial gastrectomy or jejunal resection.

There is a physiological increase in folate utilisation during pregnancy. There may be an increased utilisation in various pathological conditions, in association with inflammation or in a number of chronic haemolytic anaemias, particularly thalassaemia major, sickle cell disease and autoimmune haemolytic anaemia. Chronic folate deficiency probably predisposes patient to thrombosis, depression and neoplasia (Green and Miller, 1999).

Vitamin B₁₂ deficiency anaemia

The megaloblastic anaemia caused by vitamin B₁₂ deficiency has similar features to folate deficiency (Box 49.6). In addition to the macrocytosis, anisocytosis and poikilocytosis, there is often mild thrombocytopenia. The spleen may be slightly enlarged and there may be a slight fever. Mild jaundice may be present due to the increased breakdown of haemoglobin found in the abnormal red cells. The onset is slow and insidious, so patients often present late or are diagnosed during other investigations. The feature that separates vitamin B₁₂ deficiency from the other megaloblastic anaemias is progressive neuropathy. It is symmetrical and affects the legs rather than the arms. Patients notice a tingling in their feet and a loss of vibration sense. Occasionally, patients have muscle weakness, difficulty in walking or experience frequent falls.

Investigations

Folic acid deficiency anaemia

Many patients are symptomless initially, and the diagnosis is made following a full blood count carried out for another reason. The peripheral blood reveals large oval red cells. Anisocytosis and poikilocytosis are common. Some of the neutrophils are hypersegmented, and thrombocytopenia may be present. The red cell folate concentration accurately reflects folate stores and is a more preferable parameter than the serum folate concentration, which is subject to changes in diet and does not correlate as closely with anaemia.

Vitamin B₁₂ deficiency anaemia

Following the detection of macrocytes in the full blood count, one of the first investigations will be the determination of the serum vitamin B₁₂ level. The serum vitamin B₁₂ level is low in mild anaemia and may be very low if there is marked megaloblastic anaemia or neuropathy. If there is no concurrent folate deficiency, the serum folate level tends to be raised whilst the red cell folate level falls, possibly due to a failure of folate polyglutamate synthesis in cells. False positives (low vitamin B₁₂ level without true deficiency) may be seen in multiple myeloma, excessive ascorbic acid intake and pregnancy. In contrast, liver disease, lymphoma, autoimmune disease and myeloproliferative disorders may lead to a false-negative result (normal levels in the presence of true deficiency).

The detection of autoantibodies is helpful to distinguish pernicious anaemia from other forms. The presence of intrinsic factor antibodies is virtually diagnostic of pernicious anaemia being rarely found in any other condition. However, it is not a very sensitive test since only half the patients with pernicious anaemia have these antibodies. Gastric parietal cell antibodies are found in 85% of patients with pernicious anaemia (a more sensitive test) but unfortunately also found in up to 10% of people without pernicious anaemia (less specific) (see Table 49.5).

Table 49.5 Autoantibodies in pernicious anaemia

	Intrinsic factor antibodies	Parietal cell antibodies
Patients with pernicious anaemia	Detected in 50% of patients	Detected in 85% of patients
People who do not have pernicious anaemia	Rarely detected	Detected in up to 10%

Oral vitamin B₁₂ absorption can be measured using the Schilling test though this is now rarely used in practice as most vitamin B₁₂ deficiencies are treated in the same way. The test measures the absorption of radiolabelled oral dose of vitamin B₁₂.

Treatment

It is necessary to establish whether the patient with megaloblastic anaemia has vitamin B₁₂ deficiency or folic acid deficiency or both. Treatment of vitamin B₁₂ deficiency with folic acid may lead to the resolution of the haematological abnormalities but does not correct the neuropathy, which continues to deteriorate. If it is not possible to delay until a definitive diagnosis is made, both folic acid and vitamin B₁₂ may be given.

Folate deficiency anaemia

Folate deficiency is usually managed by replacement therapy. The duration of the treatment depends on the cause of the deficiency. Changes in dietary habits or removal of any precipitating factor should also be considered.

The normal daily requirement of folic acid is approximately 100 μcg a day; despite this, the usual treatment doses given are 5–15 mg a day. Even in malabsorption states, because of these large doses, sufficient folate is usually absorbed. Therefore, parenteral folic acid treatment is not normally required. Treatment for 4 months will normally be sufficient to ensure that folate deficient red cells are replaced.

Large doses of folic acid can produce a partial haematological response in patients with vitamin B₁₂ deficiency. The blood picture appears nearly normal but the neurological damage due to the vitamin B₁₂ deficiency continues. Folic acid therapy should not be started until vitamin B₁₂ deficiency has been excluded. It has also been suggested that patients on long-term folic acid therapy should have their vitamin B₁₂ levels checked at regular intervals (e.g. yearly).

Pregnancy

The folate requirement increases in pregnancy and is higher in twin pregnancies. Folate deficiency regularly occurs in patients with a poor diet who do not take supplements. Prophylaxis with folate (350–500 μcg daily) is now frequently given in pregnancy, often in combination with iron, starting before conception and during the first 12 weeks of pregnancy. It is important that these products with low doses of folate are not used to treat megaloblastic anaemia. Although this low-dose folate should be started before conception to prevent a first occurrence of neural tube defect, higher doses (5 mg daily) are required in women with a history of neural tube defects and again continued until week 12 (DH, 1992).

Vitamin B₁₂ deficiency anaemia

The majority of patients with vitamin B₁₂ deficiency require lifelong replacement therapy. Occasionally, specific therapy related to the underlying disorder may be all that is necessary, for example, treatment of fish tapeworm.

Since the anaemia has developed slowly, the cardiovascular system does not tolerate blood transfusions very well and is easily overloaded. Transfusions should not normally be given. In severe cases where emergency transfusion is deemed necessary, packed cells may be given slowly whilst blood (mainly plasma) is removed from the other arm. Diuretics may also need to be given, especially if the patient has congestive heart failure and poorly tolerates fluid overload.

For most patients, a definite diagnosis is made before treatment is started. The standard treatment is hydroxocobalamin 1 mg intramuscularly three times a week for 2 weeks then 1 mg every 3 months. Where there is neurological involvement, a slightly higher dose regimen is recommended, 1 mg on alternate days, until no further improvement then 1 mg every 2 months. There is no evidence that larger doses than those recommended provide any additional benefit in neuropathy. In the UK, hydroxocobalamin is the treatment of choice. It is retained in the body longer than cyanocobalamin, and reactions to it are very rare. US texts recommend cyanocobalamin rather than hydroxocobalamin because of the fear that some patients appear to develop antibodies to the vitamin B₁₂ transport protein complex in the serum. The haematological response to both is probably identical. A small amount of passive absorption of vitamin B₁₂ does take place from the gastro-intestinal tract. High (1 mg) daily oral and sublingual doses of cyanocobalamin are absorbed in sufficient quantities to manage pernicious anaemia. There have been calls for this oral regimen to replace regular injections as used in other countries. This is potentially cheaper than injections, but this indication is currently unlicensed. It may be worth considering in patients who are unable to have injections. In the UK, cyanocobalamin tablets are not available on the NHS except to treat or prevent vitamin B₁₂ deficiency in a patient who is a vegan or who has proven vitamin B₁₂ deficiency of dietary origin.

Hypokalaemia develops in some patients during the initial haematological response because potassium is an intracellular ion used in the production of new cells. Potassium supplements may be needed in the elderly and patients receiving diuretics or digoxin. The serum iron level also falls as it is incorporated into haemoglobin. The more severe the anaemia, the more likely it is to see a fall in the serum potassium or iron level.

Not only is it very gratifying to follow the response to treatment, but it is also important to monitor the response to ensure that the patient returns to normal without any attendant problems. There is often a subjective improvement before an objective one. Typically, the patient feels better within 24–48 h, and yet there may be no discernible haematological response. The first haematological change in the peripheral blood is a rise in the reticulocyte count starting around day 3 or 4 and peaking after 7–8 days. The more severe the anaemia, the higher the peak reticulocyte count. The reticulocyte count should remain raised whilst the haematocrit is less than 35%. Failure to remain raised during this time indicates the need for further evaluation. The arrest or slowing down of erythropoiesis may be due to inadequate stores of other essential factors, for example, iron, or may be due to coexisting disease such as hypothyroidism or infection.

The red cells return to normal and the platelet count rises to normal (or even higher) after 7–10 days. The haemoglobin takes much longer to return to normal. It should rise by approximately 2–3 g/dL each fortnight. Neurological damage may be irreversible. Peripheral neuropathy of recent onset often partially improves, but any spinal cord damage is irreversible even with optimum therapy.

Patient care

Folic acid deficiency anaemia

In patients who have a dietary component to their deficiency, appropriate nutritional advice should go alongside their folic acid therapy. If the cause of the deficiency has been eliminated, patients can expect to receive folic acid for approximately 4–6 months. In patients with a continuing requirement, for example, haemolytic anaemia patients can expect lifelong treatment. Those commencing folic acid therapy can anticipate feeling better after a few days but should be informed that their blood count will take much longer to return to normal.

Vitamin B₁₂ deficiency anaemia

Patients feel subjectively better very shortly after their first hydroxocobalamin injection. They can be told that their sore tongue will start to improve within 2 days and return to normal after 2–4 weeks. Patients need to be informed that they need regular injections, usually every 3 months. Surprisingly, some patients say that they feel they are ready for this injection as they approach their appointment time and feel better after their injection.

Haemolytic anaemias

In the haemolytic anaemias, there is a reduced life span of the erythrocytes. Anaemia occurs when the rate of destruction of the erythrocytes exceeds their rate of production. There are a wide range of haemolytic anaemias with both genetic and acquired disorders (Table 49.6). Only autoimmune haemolytic anaemia, sickle cell anaemia, thalassaemia and glucose-6-phosphate dehydrogenase deficiency will be briefly discussed. Haemolytic anaemias account for approximately 5% of all anaemias.

Table 49.6 Some examples of haemolytic anaemias

Genetic disorders of	Examples
Haemoglobin	Sickle cell anaemias
Haemoglobin	Thalassaemias
Energy pathways	Glucose-6-phosphate deficiency
Membrane	Hereditary spherocytosis
Membrane	Hereditary ovalcytosis
Acquired disorders
Immune	Autoimmune
Immune	Rh or ABO incompatibility
Non-immune	Infections (parasitic, bacterial)
	Drugs and chemicals
	Hypersplenism

General clinical manifestations

Patients with acute haemolytic anaemia commonly complain of malaise, fever, abdominal pain, dark urine and jaundice. They have haemoglobulinaemia, hyperbilirubinaemia, reticulocytosis and increased urobilinogen levels in the urine. Patients with chronic haemolytic anaemia also usually have splenomegaly. Their anaemia is usually normochromic and normocytic.

General treatment

Many patients with chronic haemolytic anaemia will have an over active bone marrow to compensate for the chronic haemolysis. This increases demand for folate and therefore folic acid supplements are often required, particularly for patients with a poor diet. Patients who require frequent transfusions are at risk of iron overload and require chelation therapy with desferioxamine, desferiprone or deferasirox (as previously discussed under sideroblastic anaemia).

Autoimmune haemolytic anaemia

Epidemiology

This is a range of conditions consisting of warm autoimmune haemolytic anaemia (WAIHA) and cold autoimmune haemolytic anaemia also known as cold agglutinin disease (CAD). Both forms can be subdivided into idiopathic and acquired forms, and the condition is found in all races. The most common form being idiopathic WAIHA occurring in approximately 40% of all cases with an incidence of between 1 in 4000 and 1 in 80,000. Idiopathic CAD tends to present in middle age.

Pathophysiology

The anaemia results from the presence of autoantibodies which agglutinate or lyse the patient’s own erythrocytes. In WAIHA, the haemolysis is usually extravascular and mediated by IgG. These antibodies react best at body temperature. CAD is usually mediated by IgM and is capable of fixing complement. The IgM antibody attaches to the erythrocytes and causes them to agglutinate at temperatures below 37 °C resulting in impaired blood flow to fingers, toes, nose and ears when exposed to cold.

Clinical manifestations

The symptoms in WAIHA depend on the severity of the haemolysis. In CAD, there is a range in severity of the clinical manifestations from an inconsequential laboratory finding of a benign variety to serious manifestations, such as acute haemolytic crises and Raynaud-type phenomena. A common complaint is painful fingers and toes with purplish discolouration associated with cold exposure. In chronic CAD, the patient is more symptomatic during the colder months.

Investigations

A positive direct Coomb’s test indicates the presence of antibodies to red blood cells. Further laboratory serological testing helps determine the exact nature of the reaction. Drug-induced haemolytic anaemia may be difficult to distinguish from other forms of autoimmune haemolytic anaemia, and a clear medication history will help. The antibodies produced may react with the red cells only in the presence of the drug (or one of its metabolites) or may also react without the drug being present.

Treatment

Treatment is dependent on the specific cause (Pruss et al., 2003). In WAIHA, the standard treatment is high-dose corticosteroids. Patients who do not respond can be managed with azathioprine or cyclophosphamide. Blood transfusions are necessary in severe cases, although providing blood free from underlying alloantibodies is difficult. Rituximab, the anti CD-20 monoclonal antibody, has been shown to be beneficial in some patients who fail to respond to the forementioned conventional anti-inflammatory therapy. However, this is an unlicensed indication. (D’Arena et al., 2007) Patients with CAD need to be kept warm with supportive measures as well as treated for any underlying disorder.

Sickle cell disease is a hereditary condition. Several different variants of sickle cell disease exist. It is found in a number of ethnic groups, mainly in populations that originate from tropical regions. In the UK, approximately 5000 people, largely from the Afro-Caribbean population, have sickle cell disease.

Aetiology

Patients with sickle cell disease have a different form of haemoglobin. Patients with the most common variant of sickle cell disease have haemoglobin S (Hb S). Normal haemoglobin is usually designated Hb A. Haemoglobin S has valine substituted for glutamic acid as the sixth amino acid in the β-polypeptide compared with normal haemoglobin. Patients with homozygous haemoglobin S develop many problems including anaemia.

Sickle cell trait is where a person is a carrier of the gene (heterozygous for the sickle cell gene). These people are usually asymptomatic. Sickle cell trait provides some protection from malaria and is more common in those ethnic groups originating from geographical areas that are endemic for malaria. The offspring from a father with the trait and a mother with the trait has a one in four chance of having sickle cell disease (Fig. 49.3).

Fig. 49.3 Inheritance patterns in sickle cell trait and sickle cell disease.

Pathophysiology

The membrane of red cells containing haemoglobin S is damaged, which leads to intracellular dehydration. In addition, when the patient’s blood is deoxygenated, polymerisation of haemoglobin S occurs, forming a semisolid gel. These two processes lead to the formation of crescent-shaped cells known as sickle cells. Sickle cells are less flexible than normal cells (flexibility allows normal cells to pass through the microcirculation). The inflexibility leads to impaired blood flow through the microcirculation, resulting in local tissue hypoxia. Anaemia results from an increased destruction (haemolysis) of red cells in the spleen. Some red cells in patients with sickle cell disease contain fetal haemoglobin (Hb F). These cells do not become sickle cells.

Clinical manifestations

Patients with severe variants of the disease have chronic anaemia, arthralgia, anorexia, fatigue and splenomegaly. They have crises more frequently than patients with other variants of the disease. A crisis can be precipitated by infection and fever, dehydration, hypoxia or acidosis. A combination of these factors is sometimes present. The clinical manifestation of a crisis can vary with the most common being an infarct crisis. Infarction of the long bones and larger joints or an infarction of a large organ, for example, the liver, lungs or brain, may all occur. Severe pain is a common feature, depending on the site of the infarction. Destructive bone and joint problems are frequently seen.

Investigations

The common form usually presents in the first year of life. From then on, the patients have a chronic haemolytic anaemia interspersed with crises. Abnormal haemoglobin can be detected using electrophoresis. The proportion of haemoglobin S is a useful monitoring parameter. Regular serum ferritin determinations identify the need for desferrioxamine therapy and are used to monitor progress.

Treatment

Patients with sickle cell disease have a high incidence of pneumococcal infections. A number of studies have shown the benefit of prophylactic antibiotics. Penicillin V 250 mg twice a day is usual for adults with erythromycin prescribed for patients allergic to penicillin. Administration of pneumococcal vaccine and Haemophilus influenzae vaccine is now common. Folic acid is commonly used because of the high turn over of red cells.

Attempts have been made to increase the proportion of haemoglobin F and reduce the proportion of haemoglobin S in the circulation. Several drugs (Box 49.9) have been shown (some only in animal models) to stimulate fetal haemoglobin production (Charache et al., 1995).

Box 49.9 Drugs that may increase fetal haemoglobin production

Short chain fatty acids (butyrates, valproate)

Hydroxycarbamide is effective and may reduce the frequency of crises but is limited by its cytotoxicity. Erythropoietin has been shown to increase haemoglobin F in some animal models, but this has yet to be fully demonstrated in humans. Transfusions and exchange transfusions have also been used to decrease the proportion of haemoglobin S. This is limited by the usual complications of chronic infusions: iron overload, the risk of blood-borne virus transmission and sensitisation.

Sickle cell crises require prompt and effective treatment. Removal of the trigger factor, hydration and effective pain relief are the mainstays of treatment. Appropriate antibiotic therapy should be started at the first signs of infection. Strong opioids are required for pain relief. Traditionally, many patients have been given frequent intramuscular injections of pethidine. Pethidine is not ideal since it is short acting, not very potent and repeated injections lead to the accumulation of metabolites that have been associated with seizures. Morphine is a more logical choice of opioid and has been successfully used in patient-controlled analgesia systems.

Patient care

Patients need to be encouraged to take their prophylactic penicillin and folic acid therapy regularly between crises. During a crisis, some health professionals worry about the patient developing opioid addiction. While this may happen, it is also important to recognise that crises are extremely painful and the patient requires effective analgesia.

Thalassaemias

Epidemiology

The thalassaemias are a group of inherited autosomal recessive diseases. The β thalassaemias occur mainly in populations from around the Mediterranean, North and West Africa, Middle East and Indian subcontinent. More than 100 β thalassaemia mutations have been identified, and they tend to produce severe anaemia. The α thalassaemias are more common, of which the milder variants do not cause severe anaemia, whilst the severe homozygotes lead to death in utero or infancy.

Aetiology

In α thalassaemia, there is either no α chain production (α⁰ thalassaemia) or reduced production of a chain (α⁺ thalassaemia). Similarly for β thalassaemia. Heterozygotes are usually symptomless, whilst homozygotes are more severely affected, as are compound heterozygotes in which there is a thalassaemia gene and a gene from another haemoglobin variant, for example, haemoglobin S.

Pathophysiology

In β thalassaemias, there is a reduced or absent production of the globin β chain. This leads to a relative excess of α chain which when unpaired become unstable and precipitates in the red cell precursors. There is ineffective erythropoiesis and those mature cells that reach the circulation have a shortened life span.

In α thalassaemias, the pathology is slightly different. The deficiency of α chains leads to an excess of γ or β chains. This time erythropoiesis is less affected, but the haemoglobin produced (haemoglobin Bart’s or Haemoglobin H) is unstable when the cells are in the circulation and precipitates as the cells grow older. This leads to a shortened life span with the spleen trapping many of the cells. Haemoglobin Bart’s or haemoglobin H is also physiologically useless.

Clinical manifestations

The anaemia causes erythropoietin production to increase and results in expansion of the bone marrow. In severe disease, this causes bone deformity and growth retardation. The spleen is actively involved in removing the abnormal mature cells from the circulation and becomes enlarged.

Investigations

For β thalassaemia, the diagnosis is relatively straightforward: haemolytic anaemia from infancy and racial background. Haemoglobin electrophoresis is used to determine the amounts of abnormal haemoglobin.

Treatment

There is currently no effective treatment. Patients with thalassaemia minor (those who carry the thalassaemia gene, but still make enough normal haemoglobin) usually do not require treatment. Many patients with severe forms are dependent on blood transfusions from an early age. This inevitably leads to iron overload. Desferrioxamine, deferiprone and deferasirox are routinely needed for such patients (see sideroblastic anaemia for additional information). Splenectomy helps some patients, and allogeneic stem cell transplant is used in severe cases. Prevention is actively explored with genetic counselling programmes in Italy and Greece, and antenatal screening in a number of countries.

As in sickle cell disease, much attention is being placed on the idea of switching the bone marrow to the production of fetal haemoglobin rather than the defective adult haemoglobin of β thalassaemia. It is likely that a combination of drugs (hydroxycarbamide and erythropoietin) will provide some clinical improvement.

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is a recessive hereditary disease and affects approximately 400 million people worldwide. There are more than 300 different forms of G6PD deficiency, only some of which cause anaemia. The most common form of G6PD deficiency is found in 15% of black Americans. It causes anaemia when the individual is exposed to a trigger factor. A more severe form is the Mediterranean variant of G6PD deficiency. Some of these individuals may have chronic haemolytic anaemia even in the apparent absence of exposure to a precipitating factor.

Aetiology

There are a large number of variants of G6PD activity found in different populations and ethnic groups. G6PD is an erythrocyte enzyme that is indirectly involved in the production of reduced glutathione. Glutathione is produced in response to, and protects red cells from, oxidising reagents.

Pathophysiology

G6PD is essential for the production of (NADPH) in erythrocytes. If there is a deficiency in G6PD, this decreases the production of NADPH which is needed to keep glutathione in a reduced form. Reduced glutathione helps erythrocytes deal with oxidative stress. Hence, in G6PD deficiency, if the erythrocytes are exposed to an oxidising agent, the cell membrane becomes damaged, the haemoglobin becomes oxidised and forms what are known as Heinz bodies. Some of the red cells haemolyse and others have their Heinz bodies removed by the spleen to form ‘bite cells’.

Clinical manifestation

Clinically, the two most important types of G6PD deficiency occur in the black population and in people originating from the Mediterranean. The black population has a milder form that results in an acute self-limiting haemolytic anaemia following exposure to an oxidising agent, for example, infection, acute illness, broad beans (fava) beans or drugs (Box 49.10). The haemolytic anaemia is self-limiting because the young cells produced by the bone marrow have higher levels of G6PD activity than old cells. Following exposure to the oxidising agent, the old cells are haemolysed but the new cells produced in response are more capable of tolerating the insult until they grow old. In the Mediterranean form of the disorder, the enzyme activity is very low, haemolysis is not usually self-limiting and, indeed, some patients have a chronic haemolytic anaemia despite the absence of an obvious causative factor.