HAEMOLYTIC ANEMIA

HAEMOLYSIS
The normal red cell lifespan of 120 days may be shortened by a variety of abnormalities. The bone marrow may increase its output of red cells six- to eight-fold by increasing the proportion of red cells produced. expanding the volume of active marrow and releasing reticulocytes prematurely. If the rate of destruction exceeds this increased production rate, then anaemia will develop.
The basic laboratory diagnosis of haemolysis is outlined in Figure 24.21. The red cell destruction will overload pathways for haemoglobin breakdown, causing a modest rise in unconjugated bilirubin in the blood and mild jaundice. Increased reabsorption of urobilinogen from the gut results in an increase in urinary urobilinogen (pp. 1005 and 944). Red cell destruction releases LDH and increases serum levels. The bone marrow compensation results in a reticulocytosis, and nucleated red cell precursors may also appear in the blood. The expansion of the active bone marrow may result in a neutrophilia and immature granulo¬cytes appearing in the blood to cause a leucoerythroblastic blood film. The appearances of the red cells may give an indication of the likely cause of the haemolysis. Spherocytes are small, dark-red cells and suggest autoimmune haemo¬lysis or hereditary spherocytosis; sickle cells suggest haemoglobinopathy; and red cell fragments indicate microangiopathic haemolysis.
Intravascular haemolysis
When rapid red cell destruction occurs. free haemoglobin is released into the plasma. Free haemoglobin is toxic to cells and the body has evolved binding proteins to minimise this risk. Haptoglobin is an a2-globulin produced by the liver which binds free haemoglobin, resulting in a fall in levels of haptoglobin. Once haptoglobins are saturated, free haemoglobin is oxidised to form methaemoglobin which binds to albumin, in turn forming methaemalbumin which can be detected by the Schumm s test. Methaemoglobin is degraded and any free haem is bound to a second binding protein termed haemopexin. If all the protective mechanisms are overloaded, free haemoglobin may appear in the urine. When fulminant, this gives rise to black urine as in severe falciparum malaria infection (p. 342). In smaller amounts renal tubular cells absorb the haemoglobin, degrade it and store the iron as haemosiderin. When the tubular cells are subsequently sloughed into the urine they give rise to haemosiderinuria, which is always indicative of intravascular haemolysis.
 
Extravascular haemolysis
Physiological red cell destruction occurs in the fixed reticulo-endothelial cells in the liver or spleen, so avoiding free haemoglobin in the plasma. In most haemolytic states, haemolysis is predominantly extravascular.
Features of haemolysis • T Bilirubin
• T LDH
• T Reticulocytes • .~ Haptoglobins
• T Urinary urobilinogen
• +ve urinary haemosiderin
ANAEMIAS
 
  Blood film 
 Spherocytes No spherocytes Fragmentation
DCT +O DCT O  
Autoimmune Hereditary Malaria, Hereditary Microangiopathic,
haemolysis spherocytosis Clostridium enzymopathies traumatic
Fig. 24.21 Laboratory features and classification of the causes of haemolysis. (LDH = lactate dehydrogenase; DCT = direct Coombs test)
The compensatory erythroid hyperplasia may give rise to folate deficiency, when the blood findings will be complicated by the presence of megaloblastosis. Measure¬ment of red cell folate is unreliable in the presence of haemolysis and serum folate «ill be elevated. Patients red cells can be labelled with ~-chromium: when reinjected. they can be used to determine red cell survival. or when combined with surface counting may indicate whether the liver or the spleen is the main source of red cell destruction. This is seldom performed in clinical practice_

Inherited red cell defects of structure or metabolism may result in a chronic haemolytic state. The principal patholo¬gies are red cell membrane defects (hereditan- spherocytosis or elliptocytosis), glucose-6-phosphate dehydrogenase (G6PD) deficiency and the haemoglobinopathies (p. 1035).
RED CELL MEMBRANE DEFECTS
The structure of the red cell membrane is shown in Figure 24.4 (p. 1005). The basic structure is a cytoskeleton `stapled on to the lipid bilayer by special protein complexes. This structure ensures great deformability and elasticity; the red cell diameter is 81tm but the narrowest point in the circulation is 2 ~tm in the spleen. When this normal structure is disturbed, usually by a quantitative or functional deficiency of one or more proteins in the cytoskeleton, cells lose their normal elasticity. Each time such cells pass through the spleen they lose membrane relative to their cell volume. This results in an increase in mean cell haemo¬globin concentration (MCHC), abnormal cell shape and reduced red cell survival due to extravascular haemolysis.
Hereditary spherotytosos
This is usually inherited as an autosomal dominant condition, although 25% of cases have no family history and represent new mutations. The incidence is approximately 1:5000 in developed countries but this may be an under¬estimate since the disease may present de novo in patients over 65 vears and is often discovered as a chance finding on a blood count. The pathogenesis varies between families; the most common abnormalities are deficiencies of beta spectrin or ankwrin (Fig. 24.4). The severity of spontaneous haemolvsis varies. Most cases are associated with an aswptomatic compensated chronic haemolytic state with spherocytes present on the blood film and a reticulocytosis. Occasional cases are associated with more severe haemo¬lysis; these may be due to co-incidental polymorphisms in alpha spectrin or co-inheritance of a second defect involving a different protein.
The clinical course may be complicated by crises:
0 A haemolytic crisis occurs when the severity of haemolysis increases; this is rarely seen in association with infection.
• A megaloblastic crisis follows the development of folate deficiency; this may occur as a first presentation of the disease in association with pregnancy.
• An aplastic crisis occurs in association with erythrovirus infection. Erythrovirus causes a common exanthem in children but if individuals with chronic erythroid hyperplasia become infected, the virus directly invades red cell precursors and temporarily switches off red cell production. Patients present with severe anaemia and a low reticulocyte count.
Pigment gallstones are present in up to 50% of patients and may cause symptomatic cholecystitis.
 


Investigations
The patient and other family members should be screened for features of compensated haemolysis (Fig. 24.21). This may be all that is required to confirm the diagnosis. Haemo¬globin levels are variable depending on the degree of com¬pensation. The blood film will show spherocytes but the direct Coombs test (pp. 1033-1034) is negative excluding immune haemolysis. An osmotic fragility test may show increased sensitivity to lysis in hypotonic saline solutions but is limited by lack of sensitivity and specificity. More specific flow cytometric tests detecting binding of eosin-5-maleimide to red cells are now recommended in borderline cases.
Management
Folic acid prophylaxis, 5 mg once weekly, should be given for life. Consideration may be given to splenectomy which improves but does not normalise red cell survival. Potential indications include moderate to severe haemolysis with complications (anaemia and gallstones), although splenectomy should be delayed until the child is over 6 years of age in view of the risk of sepsis. Guidelines for the management of patients after splenectomy are presented in Box .
Acute, severe haemolytic crises require transfusion support but blood must be cross-matched carefully and transfused slowly as haemolytic transfusion reactions may occur. The typical blood film appearances are masked in the presence of iron deficiency or disorders which cause a raised MCV, such as jaundice; in these situations the red cell shape is normal but spherocytes will appear when the underlying abnormality is corrected.
Hereditary elliptocytosis
This term refers to a heterogeneous group of disorders that produce an increase in elliptocytic red cells on the blood film and a variable degree of haemolysis. Hereditary elliptocytosis is due to a functional abnormality of one or more anchor proteins in the red cell membrane, e.g. alpha
24.31 MANAGEMENT OF THE SPLENECTOMISED PATIENT
Vaccinate with pneumococcal, Haemophilus influenzae type B, meningococca! group C and influenza vaccines at least 2-3 weeks before elective splenectomy. Vaccination should be given after emergency surgery, but may be less effective. Pneumococcal re-immunisation should be given at least 5-yearly and influenza annually. Vaccination status must be documented Life-long prophylactic penicillin V 250 mg 12-hourly is recommended. In penicillin-allergic patients, consider erythromycin
A card or bracelet should be carried by splenectomised patients to alert health professionals to the risk of overwhelming sepsis, wherever possible; it may be life-saving in unconscious patients by guiding the rapid administration of appropriate antibiotics
In septicaemia, splenectomised patients should be resuscitated and given intravenous antibiotics to cover pneumococcus, Haemophilus and meningococcus
The risk of malaria is increased
Animal bites should be promptly treated with local disinfection and antibiotics, to prevent serious soft tissue infection and septicaemia
 
spectrin or protein 4.1. Inheritance may be autosomal dominant or recessive. It is less common than hereditary spherocytosis in Western countries, with an incidence of 1/l0 000, but is more common in equatorial Africa and parts of South-east Asia. The clinical course is variable and depends upon the degree of membrane dysfunction caused by the inherited molecular defect(s); most cases present as an asymptomatic blood film abnormality but occasional cases result in neonatal haemolysis or a chronic compensated haemolytic state. Management of the latter is the same as for hereditary spherocytosis. A characteristic variant of hereditary elliptocytosis occurs in South-east Asia, particularlv Malaysia and Papua New Guinea, with stomatocytes and ovalocytes in the blood. This has a prevalence of up to 3017c in some communities because it offers relative protection from malaria and thus has sustained a high gene frequency. The differential diagnosis includes iron deficiencv. thalassaemia, myelofibrosis, myelodysplasia and pyruvate kinase deficiency.
RED CELL ENZYMOPATHIES
The mature red cell must produce energy via ATP to maintain a normal internal environment and cell volume whilst protecting itself from the oxidative stress presented from oxygen carriage. Anaerobic slvcolysis via the Embden-Meyerhof pathway generates ATP and the hexose monophosphate shunt produces NADPH and Qlutathione to protect against oxidative stress. The impact of functional or quantitative defects in the enzymes in these pathways will depend upon the importance of the steps affected and the presence of alternative pathways. In general. defects in the hexose monophosphate shunt result in periodic haemolysis induced by oxidative stress, whilst those in the Embden¬Meyerhof pathway result in shortened red cell survival and chronic haemolysis.
Glucose-6-phosphate dehydrogenase deficiency
This enzyme is pivotal in the hexose monophosphate shunt and produces NADPH to protect the red cell against oxidative stress. Deficiencies of this enzyme are the most common human enzymopathy, affecting 10% of the world s population with a geographical distribution which parallels the malaria belt (pp. 1035-1036) because heterozygotes are protected from malarial parasitisation. The enzyme is a heteromeric structure made of catalytic subunits which are coded for by a gene on the X chromosome. The deficiency affects males but is carried by females, who are usually only affected in the neonatal period or in the presence of extreme lyonisation or homozygosity. There are over 400 subtypes of G6PD described. The most common types associated with normal activity are the B enzyme present in most Caucasians and 70% of Afro-Caribbeans, and the A variant present in 20% of Afro-Caribbeans. The two common variants associated with reduced activity are the A- variety in approximately 10% of Afro-Caribbeans, and the Medi¬terranean or B- variety in Caucasians. In East and West Africa up to 20% of males and 4% of females (homozy¬gotes) are affected and have enzyme levels of approximately
ANAEMIAS
24.32 GLUCOSE-6-DEHYDROGENASE DEFICIENCY
Clinical features
Acute drug-induced haemolysis to (e.g.)
• Analgesics: aspirin, phenacetin
• Antimalarials: primaquine, quinine, chloroquine, pyrimethamine
• Antibiotics: sulphonamides, nitrofurantoin, ciprofloxacin
• Miscellaneous: quinidine, probenecid, vitamin K, dapsone
Chronic compensated haemolysis
Infection or acute illness
Neonatal jaundice
• May be a feature of the B- enzyme
Favism or acute haemolysis after ingestion of the broad bean
Vicia faba i
Laboratory features
Non-spherocytic intravascular haemalysis during an attack
The blood film will show:
• Bite cells (red cells with a `bite of membrane missing)
• Blister cells (red cells with surface blistering of the membrane)
• Irregularly shaped small cells
• Polychromasia reflecting the reticulocytosis
• Denatured haemoglobin visible as Heinz bodies within the red
cell cytoplasm, if stained with a supravital stain such as methyl
violet
G6PD level
• Can be indirectly assessed by screening methods which usually
depend upon the decreased ability to reduce dyes
• Direct assessment of G6PD is made in those with low screening
values
• Care must be taken close to an acute haemolytic episode
because reticulocytes may have normal enzyme levels and give
rise to a false normal result
by lead and this is the reason why basophilic stippling is a feature of lead poisoning.