Hoffbrand's Essential Haematology 8th Edition 2020-24-38 PDF

12 / Chapter 2: Erythropoiesis and general aspects of anaemia Blood cells We each make approximately 1012 new erythrocytes (red cells) each day by the complex and finely...

12 / Chapter 2: Erythropoiesis and general aspects of anaemia Blood cells We each make approximately 1012 new erythrocytes (red cells) each day by the complex and finely regulated process All the circulating blood cells derive from pluripotential stem of erythropoiesis. Erythropoiesis passes from the stem cell cells in the marrow. They divide into three main types. The most through the progenitor cells, colony-forming unit (CFU), numerous are red cells, which are specialized for the carriage of erythroid and megakaryocyte (CFUMkE), burst-forming unit oxygen from the lungs to the tissues and of carbon dioxide in erythroid (BFUE) and erythroid CFU (CFUE; Fig. 1.2) to the the reverse direction (Table 2.1). They have a 4-month lifespan, first recognizable erythrocyte precursor in the bone marrow, whereas the smallest cells, platelets involved in haemostasis, the pronormoblast (Fig. 2.2). This process occurs in an eryth- circulate for only 10 days. The white cells are made up of four roid niche in which about 30 erythroid cells at various stages of types of phagocyte: neutrophils, eosinophils, basophils and development surround a central macrophage. monocytes, which protect against bacterial and fungal infec- The pronormoblast is a large cell with dark blue cyto- tions (see Chapter 8); and of lymphocytes, which include B plasm, a central nucleus with nucleoli and slightly clumped cells, involved in antibody production, T cells (CD4 helper chromatin (Fig. 2.2). It gives rise to a series of progressively and CD8 suppressor), concerned with the immune response smaller normoblasts by a number of cell divisions. They also and in protection against viruses and other foreign cells, and contain progressively more haemoglobin (which stains pink) natural killer cells, a subset of CD8 T cells (see Chapter 9). in the cytoplasm; the cytoplasm stains paler blue as it loses its White cells have a wide range of lifespan (Table 2.1). RNA and protein synthetic apparatus, while nuclear chroma- The red cells and platelets are counted and their diameter tin becomes more condensed (Figs 2.2 and 2.3). The nucleus and other parameters measured by an automated cell counter is finally extruded from the late normoblast within the marrow (Fig. 2.1). The counter also enumerates the different types of and a reticulocyte results, which still contains some ribosomal white cell by flow cytometry and detects abnormal cells. RNA and is still able to synthesize haemoglobin (Fig. 2.4). Table 2.1 The blood cells. Cell Diameter (μm) Lifespan in blood Number Function Red cells 6–8 120 days Male: 4.5–6.5 × 1012/L Oxygen and carbon dioxide Female: 3.9–5.6 × 1012/L transport Platelets 0.5–3.0 10 days 140–400 × 109/L Haemostasis Phagocytes Neutrophils 12–15 6–10 h 1.8–7.5 × 109/L Protection from bacteria, fungi Monocytes 12–20 20-40 h 0.2–0.8 × 109/L Protection from bacteria, fungi Eosinophils 12–15 Days 0.04–0.44 × 109/L Protection against parasites Basophils 12–15 Days 0.01–0.1 × 109/L Lymphocytes 7–9 (resting) Weeks or years 1.5–3.5 × 109/L B cells: immunoglobulin 12–20 (active) synthesis T cells: protection against B      T viruses; immune functions Natural killer cells 10 (resting ) Hours or days 0.1–0.4 Protection against virus- 10–20 (active) infected and neoplastic cells NK  Chapter 2: Erythropoiesis and general aspects of anaemia / 13 Automated cell counter Neutrophils Flow cytometry Eosinophils Platelet Red cell – white cell Basophils count count differentiatial Monocytes and size and size Lymphocytes Computer Lysis of screen red cells Whole blood in EDTA Bar code Printer Specimen tubes in rack on a track Bar code reader Figure 2.1 Automated blood cell counter. Source: A.B. Mehta, A.V. Hoffbrand (2014) Haematology at a Glance, 4th edn. Reproduced with permission of John Wiley & Sons. (a) (b) (c) (d) Figure 2.2 Erythroblasts (normoblasts) at varying stages of development. The earlier cells are larger, with more basophilic cytoplasm and a more open nuclear chromatin pattern. The cytoplasm of the later cells is more eosinophilic as a result of haemoglobin formation. 14 / Chapter 2: Erythropoiesis and general aspects of anaemia Pronormoblast Early 60–80% in cell cycle BONE MARROW Intermediate (polychromatic) Late (pyknotic) Reticulocytes Post-mitotic non-dividing BLOOD Red cells Figure 2.3 The amplification and maturation sequence in the development of mature red cells from the pronormoblast. This cell is slightly larger than a mature red cell, and circulates the marrow (extramedullary erythropoiesis) and also with some in the peripheral blood for 1–2 days before maturing, when marrow diseases. RNA is completely lost. A completely pink-staining mature erythrocyte results, which is a non-nucleated biconcave disc (see Fig. 24.3). One pronormoblast usually gives rise to 16 Erythropoietin mature red cells (Fig. 2.3). Nucleated red cells (normoblasts) are not present in normal human peripheral blood (Fig. 2.4). Erythropoiesis is regulated by the hormone erythropoie- They appear in the blood if erythropoiesis is occurring outside tin, a heavily glycosylated polypeptide. Normally, 90% of the hormone is produced in the peritubular interstitial cells of the kidney and 10% in the liver and elsewhere. There are no Normoblast Reticulocyte Mature preformed stores and the stimulus to erythropoietin produc- RBC tion is the oxygen (O2) tension in the tissues of the kidney (Fig. 2.5). Hypoxia induces synthesis of hypoxia-inducible factors (HIF-1α and β), which stimulate erythropoietin pro- duction and also new vessel formation and transferrin recep- tor synthesis, and reduce hepcidin synthesis, increasing iron Nuclear DNA Yes No No absorption. Von Hippel-Lindau (VHL) protein breaks down HIFs and PHD2 hydroxylates HIF-1α, allowing VHL binding RNA in cytoplasm Yes Yes No (Fig. 2.5). Mutations in the genes for these proteins may cause polycythaemia (see Chapter 15). In marrow Yes Yes Yes Erythropoietin production therefore increases in anaemia, and also when haemoglobin for some metabolic or structural In blood No Yes Yes reason is unable to give up O2 normally, when atmospheric O2 is low or when defective cardiac or pulmonary function or damage to the renal circulation affects O2 delivery to the Figure 2.4 Comparison of the DNA and RNA content, and marrow kidney. and peripheral blood distribution, of the erythroblast (normoblast), Erythropoietin stimulates erythropoiesis by increasing reticulocyte and mature red blood cell (RBC). the number of progenitor cells committed to erythropoiesis.  Chapter 2: Erythropoiesis and general aspects of anaemia / 15 Bone marrow Stem cells Early BFU-E Late BFU-E CFU-E (Pro)normoblasts Reticulocyte Circulating Erythropoietin red cells Peritubular interstitial cells of outer cortex O2 delivery O2 sensor (HIFα and β) Atmospheric O2 O2-dissociation curve Cardiopulmonary function Kidney Haemoglobin concentration Renal circulation Figure 2.5 The production of erythropoietin by the kidney in response to its oxygen (O2) supply. Erythropoietin stimulates erythropoiesis and so increases O2 delivery. BFUE, erythroid burst-forming unit; CFUE, erythroid colony-forming unit. Hypoxia induces hypoxia inducible factors (HIFs) α and β, which stimulate erythropoietin production. Von-Hippel–Lindau (VHL) protein breaks down HIFs. PHD2 (prolyl hydroxylase) hydroxylates HIF-1α, allowing VHL binding to HIFs. Mutations in VHL, PHD2 or HIF-1α underlie congenital polycythaemia (see p. 189). The transcription factor GATA2 is involved in initiating Indications for erythropoietin therapy erythroid differentiation from pluripotential stem cells. Sub- Recombinant erythropoietin is needed for treating anaemia sequently the transcription factors GATA1 and FOG1 are resulting from renal disease or from various other causes. It activated by erythropoietin receptor stimulation and are is given subcutaneously either three times weekly, once every important in enhancing expression of erythroid-specific genes 1–2 weeks or every 4 weeks, depending on the indication and (e.g. globin, haem biosynthetic and red cell membrane pro- on the preparation used (erythropoietin alpha or beta; darb- teins) and also enhancing expression of anti-apoptotic genes epoetin alpha, a heavily glycosylated longer-acting form; or and of the transferrin receptor (CD71). Late BFUE and CFUE, Micera, the longest-acting preparation). The main indication is which have erythropoietin receptors, are stimulated to prolif- end-stage renal disease (with or without dialysis). The patients erate, differentiate and produce haemoglobin. The proportion often also need oral or intravenous iron. Other indications are of erythroid cells in the marrow increases and, in the chronic listed in Table 2.2. The haemoglobin level and quality of life state, there is anatomical expansion of erythropoiesis into fatty may be improved. A low serum erythropoietin level prior to marrow and sometimes into extramedullary sites. In infants, treatment is valuable in predicting an effective response. Side the marrow cavity may expand into cortical bone, resulting in effects include a rise in blood pressure, thrombosis and local bone deformities with frontal bossing and protrusion of the injection site reactions. It has been associated with progression maxilla (see p. 85). of some tumours which express EPO receptors. Conversely, increased O2 supply to the tissues (because of The marrow requires many other precursors for effective an increased red cell mass or because haemoglobin is able to erythropoiesis. These include metals such as iron and cobalt, release its O2 more readily than normal) reduces the erythro- vitamins (especially vitamin B12, folate, vitamin C, vitamin E, poietin drive. Plasma erythropoietin levels can be valuable in vitamin B6, thiamine and riboflavin) and hormones such as clinical diagnosis. They are high in anaemia, unless this is due to androgens and thyroxine. Deficiency in any of these may be renal failure or if a tumour-secreting erythropoietin is present, associated with anaemia. but low in severe renal disease or polycythaemia vera (Fig. 2.6). 16 / Chapter 2: Erythropoiesis and general aspects of anaemia Table 2.3 Normal haemoglobins in adult blood. 105 Normal Hb A Hb F Hb A2 Anaemias Renal failure: Structure α2β2 α2γ2 α2δ2 Nephric Normal (%) 96–98 0.5–0.8 1.5–3.2 Anephric 104 the specialized protein haemoglobin. Each molecule of normal adult haemoglobin A (Hb A, the dominant haemoglobin in blood after the age of 3–6 months) consists of four polypep- tide chains, α2β2, each with its own haem group. Normal adult EPO (mIU/mL) blood also contains small quantities of two other haemoglob- 103 ins: Hb F and Hb A2. These also contain α chains, but with γ and δ chains, respectively, instead of β (Table 2.3). The syn- thesis of the various globin chains in the fetus and adult is dis- cussed in more detail in Chapter 7. Haem synthesis occurs largely in the mitochondria by a series of biochemical reactions, commencing with the con- 102 densation of glycine and succinyl coenzyme A under the action of the key rate-limiting enzyme δ-aminolaevulinic acid (ALA) synthase (Fig. 2.7). Pyridoxal phosphate (vitamin B6) is a coenzyme for this reaction. The main sources of succinyl CoA are glutamine and glucose, which are converted to alpha-­ ketoglutarate, a succinate precursor inside the erythroid cells. 101 Ultimately, protoporphyrin combines with iron in the ferrous 40 60 80 100 120 140 160 180 Haemoglobin in g/L Transferrin Figure 2.6 The relation between erythropoietin (EPO) in plasma and haemoglobin concentration. Anaemias exclude conditions shown to be associated with impaired production of EPO. Source: Transferrin Amino acids Modified from M. Pippard et al. (1992) Br. J. Haematol. 82: 445. cycle Reproduced with permission of John Wiley & Sons. Ribosomes Table 2.2 Clinical indications (in selected subjects) for Fe α and β chains erythropoietin. Ferritin Anaemia of chronic renal disease Mitochondrion α2β2 globin Myelodysplastic syndrome Glycine + B6 Fe + Succinyl CoA Haem (x4) Anaemia associated with malignancy and chemotherapy Proto- δALA porphyrin Anaemia of chronic diseases, e.g. rheumatoid arthritis Haemoglobin Anaemia of prematurity Porphobilinogen Coproporphyrinogen Perioperative uses Uroporphyrinogen Haemoglobin Figure 2.7 Haemoglobin synthesis in the developing red cell. The Haemoglobin synthesis mitochondria are the main sites of protoporphyrin synthesis, iron (Fe) is supplied from circulating transferrin and globin chains are The main function of red cells is to carry O2 to the tissues synthesized on ribosomes. δ-ALA, δ-aminolaevulinic acid; CoA, and to return carbon dioxide (CO2) from the tissues to the coenzyme A. lungs. In order to achieve this gaseous exchange they contain  Chapter 2: Erythropoiesis and general aspects of anaemia / 17 CH2 100 Arterial O2 tension CH CH3 H C Mean venous α O2 tension H 3C CH CH2 2,3-DPG 75 2,3-DPG H+ % saturation haemoglobin N N H+ CO2 HbF HbS HCδ Fe βCH N N 50 P50 H3C CH3 γ C H CH2 CH2 25 Globin CH2 CH2 COOH COOH 0 0 25 50 75 100 Figure 2.8 The structure of haem. PO2 Figure 2.10 The haemoglobin oxygen (O2) dissociation curve. (Fe2+) state to form haem (Fig. 2.8). A tetramer of four globin 2,3-DPG, 2,3-diphosphoglycerate. chains, each with its own haem group in a ‘pocket’, is then formed to make up a haemoglobin molecule (Fig. 2.9). Haemoglobin function The red cells in systemic arterial blood carry O2 from the lungs O2 at which haemoglobin is half saturated with O2) of normal to the tissues and return in venous blood with CO2 to the blood is 26.6 mmHg. With increased affinity for O2, the curve lungs. As the haemoglobin molecule loads and unloads O2, shifts to the left (i.e. the P50 falls), while with decreased affinity the individual globin chains move on each other (Fig. 2.9). for O2, the curve shifts to the right (i.e. the P50 rises). The α1β1 and α2β2 contacts stabilize the molecule. When O2 Normally, in vivo, O2 exchange operates between 95% is unloaded the β chains are pulled apart, permitting entry of saturation (arterial blood) with a mean arterial O2 tension of the metabolite 2,3-diphosphoglycerate (2,3-DPG), resulting 95 mmHg and 70% saturation (venous blood) with a mean in a lower affinity of the molecule for O2. This movement is venous O2 tension of 40 mmHg (Fig. 2.10). responsible for the sigmoid form of the haemoglobin O2 dis- The normal position of the curve depends on the concen- sociation curve (Fig. 2.10). The P50 (i.e. the partial pressure of tration of 2,3-DPG, H+ ions and CO2 in the red cell and on the structure of the haemoglobin molecule. High concentrations of 2,3-DPG, H+ or CO2, and the presence of sickle haemo- globin (Hb S), shift the curve to the right (oxygen is given up more easily), whereas fetal haemoglobin (Hb F) – which is α1 β1 α1 β1 unable to bind 2,3-DPG – and certain rare abnormal haemo- O2 O2 globins associated with polycythaemia shift the curve to the left, because they give up O2 less readily than normal. G DP Methaemoglobinaemia 3- 2, This is a clinical state in which circulating haemoglobin is O2 O2 present with iron in the oxidized (Fe3+) instead of the usual β2 α2 β2 α2 Fe2+ state. It may arise because of a hereditary deficiency of methaemoglobin reductase or inheritance of a structurally Oxyhaemoglobin Deoxyhaemoglobin Haem abnormal haemoglobin (Hb M). Hb Ms contain an amino acid substitution affecting the haem pocket of the globin chain. Toxic methaemoglobinaemia (and/or sulphaemoglobi- Figure 2.9 The oxygenated and deoxygenated haemoglobin naemia) occurs when a drug or other toxic substance oxidizes molecule. α, β, globin chains of normal adult haemoglobin (Hb A); haemoglobin. In all these states, the patient is likely to show 2,3-DPG, 2,3-diphosphoglycerate. cyanosis. 18 / Chapter 2: Erythropoiesis and general aspects of anaemia The red cell generated. This ATP provides energy for maintenance of red cell volume, shape and flexibility. In order to carry haemoglobin into close contact with the The Embden–Meyerhof pathway also generates NADH, tissues and for successful gaseous exchange, the red cell, 8 μm in which is needed by the enzyme methaemoglobin reductase to diameter, must be able to pass repeatedly through the microcir- reduce functionally dead methaemoglobin containing ferric culation, whose minimum diameter is 3.5 μm; to maintain hae- iron (produced by oxidation of approximately 3% of haemo- moglobin in a reduced (ferrous) state; and to maintain osmotic globin each day) to functionally active, reduced haemoglo- equilibrium despite the high concentration of protein (haemo- bin containing ferrous ions. The Luebering–Rapoport shunt, globin) in the cell. A single journey round the body takes 20 or side arm, of this pathway (Fig. 2.11) generates 2,3-DPG, seconds and its total journey throughout its 120-day lifespan important in the regulation of haemoglobin's oxygen affinity has been estimated to be 480 km (300 miles). To fulfil these (Fig. 2.9). functions, the cell is a flexible biconcave disc with an ability to generate energy as adenosine triphosphate (ATP) by the anaero- Hexose monophosphate (pentose bic glycolytic (Embden–Meyerhof ) pathway (Fig. 2.11) and to phosphate) shunt generate reducing power as nicotinamide adenine dinucleotide (NADH) by this pathway and as reduced nicotinamide adenine Approximately 10% of glycolysis occurs by this oxida- dinucleotide phosphate (NADPH) by the hexose monophos- tive pathway in which glucose-6-phosphate is converted to phate shunt (see Fig. 6.6). 6-­phosphogluconate and so to ribulose-5-phosphate (see Fig. 6.6). NADPH is generated and is linked with glutathione, which Red cell metabolism maintains sulphydril (SH) groups intact in the cell, including those in haemoglobin and the red cell membrane. In one of the Embden–Meyerhof pathway most common inherited abnormalities of red cells, glucose-6-­ In this series of biochemical reactions, glucose that enters the phosphate dehydrogenase (G6PD) deficiency, the red cells are red cell from plasma by facilitated transfer is metabolized to extremely susceptible to oxidant stress (see p. 70). lactate (Fig. 2.11). For each molecule of glucose used, two mol- ecules of ATP and thus two high-energy phosphate bonds are Red cell membrane The red cell membrane comprises a lipid bilayer, integral mem- Glucose brane proteins and a membrane skeleton (Fig. 2.12). Approxi- mately 50% of the membrane is protein, 20% phospholipids, 20% cholesterol molecules and up to 10% is carbohydrate. Glucose-6-P Carbohydrates occur only on the external surface, while pro- G6PD Hexose monophosphate teins are either peripheral or integral, penetrating the lipid shunt bilayer. Several red cell proteins have been numbered accord- Fructose-6-P ing to their mobility on polyacrylamide gel electrophoresis Generation of NADPH (PAGE), e.g. band 3, proteins 4.1, 4.2 (Fig. 2.12). (see Fig 6.6) The membrane skeleton is formed by structural proteins that include α and β spectrin, ankyrin, protein 4.1 and actin. These proteins form a horizontal lattice on the internal side of 1,3 DPG the red cell membrane and are important in maintaining the biconcave shape. Spectrin is the most abundant and consists 2,3 DPG of two chains, α and β, wound around each other to form Luebering- Rapoport heterodimers, which then self-associate head to head to form 3 PG shunt tetramers. These tetramers are linked at the tail end to actin and are attached to protein band 4.1. At the head end, the Generation Pyruvate β spectrin chains attach to ankyrin, which connects to band of NADH 3, the transmembrane protein that acts as an anion channel (‘vertical connections’; Fig. 2.12). Protein 4.2 enhances this Lactate interaction. Defects of the membrane proteins explain some of the abnormalities of shape of the red cell membrane (e.g. hered- Figure 2.11 The Embden–Meyerhof glycolytic pathway. The itary spherocytosis and elliptocytosis; see Chapter 6), while Luebering–Rapoport shunt regulates the concentration of 2,3- alterations in lipid composition because of congenital or diphosphoglycerate (2,3-DPG) in the red cell. ATP, adenosine acquired abnormalities in plasma cholesterol or phospholipid triphosphate; NAD, NADH, nicotinamide adenine dinucleotide; may be associated with other membrane abnormalities (see PG, phosphoglycerate. Fig. 2.16).  Chapter 2: Erythropoiesis and general aspects of anaemia / 19 Band 3 Glycophorin B protein Glycophorin C Membrane phospholipid Glycophorin A Vertical interaction 4.2 4. 1 Actin Cholesterol Ankyrin 4. 1 Tropomyosin Cytoskeleton α Spectrin β Spectrin Horizontal interaction Figure 2.12 The structure of the red cell membrane. Some of the penetrating and integral proteins carry carbohydrate antigens; other antigens are attached directly to the lipid layer. Anaemia Global incidence Anaemia is defined as a reduction in the haemoglobin The World Health Organization defines anaemia in adults as a concentration of the blood below normal for age and sex haemoglobin less than 130 g/L in males and less than 120 g/L (Table 2.4). Although normal values can vary between labora- in females. On this basis, anaemia was estimated in 2010 to tories, typical values would be less than 135 g/L in adult males occur in about 33% of the global population. Prevalence was and less than 115 g/L in adult females (Fig. 2.13). From the greater in females than males at all ages and most frequent in age of 2 years to puberty, less than 110 g/L indicates anaemia. children less than 5 years old. Anaemia was most frequent in As newborn infants have a high haemoglobin level, 140 g/L is South Asia, and Central, West and East Sub-Saharan Africa. taken as the lower limit at birth (Fig. 2.13). Anaemia in preg- The main causes are iron deficiency (life-long poor diet com- nancy and neonates is discussed in Chapter 31. bined with menstruation and/or repeated pregnancies, hook- Alterations in total circulating plasma volume as well worm, schistosomiasis), the anaemia of chronic disorders (see as in total circulating haemoglobin mass determine the hae- p. 38), sickle cell diseases, thalassaemia and malaria. moglobin concentration. Reduction in plasma volume (as in dehydration) may mask anaemia or even cause (apparent, pseudo) polycythaemia (see p. 185); conversely, an increase in Clinical features of anaemia plasma volume (as with splenomegaly or pregnancy) may cause The major adaptations to anaemia are in the cardiovascular anaemia even with a normal total circulating red cell and hae- system (with increased stroke volume and tachycardia) and moglobin mass. in the haemoglobin O2 dissociation curve. In some patients After acute major blood loss, anaemia is not immediately with quite severe anaemia there may be no symptoms or signs, apparent because the total blood volume is reduced. It takes whereas others with mild anaemia may be severely incapaci- up to a day for the plasma volume to be replaced and so for tated. The presence or absence of clinical features can be con- the degree of anaemia to become apparent (see p. 385). Regen- sidered under four major headings. eration of red cells and haemoglobin mass takes substantially 1 Speed of onset Rapidly progressive anaemia causes more longer. The initial clinical features of major blood loss are symptoms than anaemia of slow onset, because there is less therefore a result of reduction in blood volume rather than of time for adaptation in the cardiovascular system and in the anaemia. O2 dissociation curve of haemoglobin. 20 / Chapter 2: Erythropoiesis and general aspects of anaemia Table 2.4 Normal values for blood cells and haematinics. 140 Neonates Men Males Females 130 Haemoglobin (g/L) Haemoglobin (g/L) 135.0–175.0 115.0–155.0 Infants 120 Red cells (erythrocytes) 4.5–6.5 3.9–5.6 Women (× 1012/L) 110 Children PCV (haematocrit) (%) 40–52 36–48 100 Mean cell volume (MCV) (fL) 80–95 90 Mean cell haemoglobin 27–34 1 2 3 1 5 10 20 30 40 50 60 70 (MCH) (pg) Age: Months Years Reticulocyte count (× 109/L) 50–150 White cells (leucocytes) Figure 2.13 The lower limit of normal blood haemoglobin concentration in men, women and children of various ages. Total (× 109/L) 4.0–11.0 Neutrophils (× 109/L) 1.8–7.5* is particularly marked in some anaemias that either raise 2,3-DPG directly, e.g. pyruvate kinase deficiency (p. 72), Lymphocytes (× 109/L) 1.5–3.5 or that are associated with a low-affinity haemoglobin, e.g. Monocytes (× 109/L) 0.2–0.8 Hb S (see Fig. 2.10). Eosinophils (× 109/L) 0.04–0.44 Symptoms Basophils (× 109/L) 0.01–0.1 If the patient does have symptoms these are usually shortness Platelets (× 10 /L) 9 150–400 of breath, particularly on exertion, weakness, lethargy, palpi- tation and headaches. In older subjects, symptoms of cardiac Serum iron (μmol/L) 10–30 failure, angina pectoris or intermittent claudication or con- Total iron-binding capacity 40–75 (2.0–4.0 g/L as fusion may be present. Visual disturbances because of retinal (μmol/L) transferrin) haemorrhages may complicate very severe anaemia, particu- larly of rapid onset (Fig. 2.14). Serum ferritin** (μg/L) 40–340 14–150 Serum vitamin B12** (ng/L) 160—925 (20–680 pmol/L) Signs These may be divided into general and specific. General signs Serum folate** (μg/L) 3.0–15.0 (4–30 nmol/L) include pallor of mucous membranes or nail beds, which Red cell folate** (μg/L) 160–640 (360–1460 nmol/L) * Lower limit 1.5 × 109/L in some ethnic groups, e.g. in Middle East and black-skinned people. ** Normal ranges differ between different laboratories. PCV, packed cell volume. 2 Severity Mild anaemia often produces no symptoms or signs, but these are usually present when the haemoglobin is less than 90 g/L. Even severe anaemia (haemoglobin con- centration as low as 60 g/L) may produce remarkably few symptoms, when there is very gradual onset in a young sub- ject who is otherwise healthy. 3 Age The elderly tolerate anaemia less well than the young because normal cardiovascular compensation is impaired. 4 Haemoglobin O2dissociation curve Anaemia, in general, is associated with a rise in 2,3-DPG in the red cells and Figure 2.14 Retinal haemorrhages in a patient with severe a shift in the O2 dissociation curve to the right, so that anaemia (haemoglobin 25 g/L) caused by severe haemorrhage. oxygen is given up more readily to tissues. This adaptation  Chapter 2: Erythropoiesis and general aspects of anaemia / 21 (a) (b) Figure 2.15 Pallor of the conjunctival mucosa (a) and of the nail bed (b) in two patients with severe anaemia (haemoglobin 60 g/L). occurs if the haemoglobin level is less than 90 g/L (Fig. 2.15). The association of features of anaemia with excess infec- Conversely, skin colour is not a reliable sign. A hyperdynamic tions or spontaneous bruising suggests that neutropenia or circulation may be present with tachycardia, a bounding pulse, thrombocytopenia may be present, possibly as a result of bone cardiomegaly and a systolic flow murmur, especially at the marrow failure. apex. Particularly in the elderly, features of congestive heart failure may be present. Classification and laboratory findings in anaemia Specific signs are associated with particular types of Red cell indices anaemia, e.g. koilonychia (spoon nails) with iron deficiency, jaundice with haemolytic or megaloblastic anaemias, leg The most useful classification is that based on red cell indices ulcers with sickle cell and other haemolytic anaemias, or bone (Table 2.4). This divides the anaemia into microcytic, nor- deformities with thalassaemia major. mocytic and macrocytic (Table 2.5). As well as suggesting Table 2.5 Classification of anaemia. Microcytic, hypochromic Normocytic, normochromic Macrocytic MCV 95 fL MCH