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Understanding haemolytic anaemia
Symposium: Haematology
Understanding haemolytic anaemia
Haemolysis Lysis of RBCs is part of the daily physiological process of RBC turnover. However, the term ‘haemolysis’ is used when referring to the accelerated, pathological forms of haemolysis that result in anaemia and jaundice.
Georgina W Hall
Normal haemolysis Maintaining normal haemoglobin levels – the role of the reticulocyte: RBC production (erythropoiesis) involves a constant turnover of cells. Normally, effete red cells are lysed at the end of their life by macrophages in the reticuloendothelial system (RES) mainly in the bone marrow but also in the liver and spleen. This process is known as extravascular haemolysis; that is, the lysis does not occur intravascularly in the blood vessels. The normal lifespan of an RBC is 100–120 days. This process of natural wastage is controlled and balanced. As an old cell is removed, a new RBC, the reticulocyte, recently rid of its nucleus but still replete with RNA and synthetic abilities, appears in the blood fresh from the bone marrow ready to spend the next 100 days or so working in the peripheral blood. Normally, 1–2% of circulating RBCs are reticulocytes, and this small proportion is all that is required to maintain a normal haemoglobin level in the steady state. The reason why anaemia does not occur normally is that there is a balance between destruction and repopulation that is controlled by various physiological mechanisms (oxygen sensors and production of erythropoietin (Epo) in the kidney).
Abstract Understanding haemolytic anaemia means understanding the pathophysiology of accelerated red blood cell (RBC) lysis. Clinicians need to be aware of the different types of haemolysis, intravascular and extravascular, and the causes, both inherited and acquired. Appreciation of these facts will ensure that appropriate first-line investigations are performed in jaundiced anaemic children when they first present. Specialist advice should then be obtained to ensure the best management of these children. Acute and often self-limiting forms of haemolysis can be the most dramatic and these are the forms most likely to present to the general paediatrician.
Keywords haemolysis; hereditary and acquired; immune and non-immune haemolytic anaemia; intravascular and extravascular; haemoglobinuria; reticulocytosis
Physiology of RBC production: In the bone marrow, stem cell progenitors with Epo receptors become committed to erythropoiesis. This commitment is increased (i.e. more progenitors are pushed into RBC production as opposed to making white blood cells (WBCs) or platelets) when there are higher levels of circulating Epo (analogous to car production in factory when there is an increased demand for red cars). Increased production of Epo from the kidney occurs when the oxygen tension in the kidney, for whatever reason, declines. These committed progenitors differentiate and grow through the various stages of development (pro-normoblast to normo(erythro)blasts – early, intermediate and late) until they eject their nucleus and become reticulocytes.
Introduction Understanding haemolytic anaemias requires a knowledge of both the physiology of red blood cell (RBC) production and breakdown, and the pathophysiology of haemolysis. Clinicians who understand haemolysis can investigate, intelligently a jaundiced, anaemic child. Most paediatricians see cases of haemolysis during their time on the neonatal unit and while doing acute on-call for paediatrics. However, most children with chronic or hereditary forms of haemolysis are under specialist care, often with open-door access, and are therefore seen predominantly by those working in haematology units rather than by general paediatricians. After reacquainting the clinician with basic RBC physiology and the pathophysiology of RBC lysis, this review discusses the various types and causes of haemolysis, both hereditary and acquired. More detailed information can be obtained from the recommended Further Reading. Management of a jaundiced/ anaemic child depends on the underlying cause. The presentation, ethnic origin and family history of each patient should lead to a suspicion of the most likely diagnosis and hence the appropriate investigations. The advice and support of a haematologist should always be sought, and in difficult cases the (paediatric) haematologist should be the lead for the care of the child.
Physiology of RBC breakdown: The breakdown of an RBC is in part a recycling process (Figure 1), and understanding this physiological process makes understanding haemolysis easy. The haemoglobin is broken down into haem and globin. The haem is broken down into iron, which is bound and transferred by transferrin to the marrow erythroblasts (primitive RBCs growing in the bone marrow) and protoporphyrin, which is broken down mainly into bilirubin with some carbon monoxide (which is expired via the lungs). Remembering what happens to the bilirubin is essential in understanding how to investigate haemolysis. Bilirubin is normally circulated to the liver where it is conjugated to bilirubin glucuronides, which are excreted into the gut via the bile and converted to stercobilionogen and stercobilin, which are excreted in the faeces. Some stercobiliogen and stercobilin is reabsorbed and excreted in the urine as urobilinogen and
Georgina W Hall PhD FRCP FRCPath FRCPCH is Consultant Paediatric Haematologist at the Department of Paediatric Haematology/Oncology, Oxford Children’s Hospital, Headington, Oxford OX3 9DU, UK.
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would reveal marked erythroid hyperplasia; that is, a massive increase in RBC production. In acute and profound anaemia, nucleated RBCs (late normoblasts; the stage just before reticulocytes, normally only seen in the peripheral blood of neonates and in the bone marrow of everyone else) also appear in the peripheral blood. The result of this massive surge in activity is to bring the haemoglobin level back to normal, at which point the marrow and reticulocyte count can settle back down to normal activity, provided the destructive process has ceased. Note that in some very acute forms of brisk haemolysis, there is often a delay in the reticulocyte response and confusion may arise as to whether the anaemia is reticulocytopenic, as may be seen in transient erythroblastopenia of childhood (TEC), or even Diamond Blackfan anaemia (DBA). However, obvious signs of haemolysis, if they are still present, usually allay such fears (Table 1).
Haemoglobin
Haem
Globin
Protoporphyrin
Iron
Amino acids
Bilirubin (free)
CO
Transferrin
Liver
Bilirubin glucuronides
Bone marrow
Red cell precursors: Erythroblasts
Compensated haemolysis Depending on the degree or chronicity of the process, haemolytic anaemia can be compensated; that is, the reticulocyte response is such that the haemoglobin is maintained within the normal range and the patient is not anaemic (though he or she may be jaundiced) despite ongoing haemolysis. A normal marrow, working effectively and producing normal RBCs can produce cells at 6–8 times the normal rate in the face of increased destruction. Patients with ineffective erythropoiesis (whose marrows are unable to make normal cells) cannot mount such a response and often become profoundly anaemic quite dramatically. An example of this is a parvovirus-induced aplastic crisis in a patient with a chronic haemolytic anaemia such as hereditary spherocytosis (HS) or sickle cell disease). In these patients, so dependent on a high reticulocyte count, their haemoglobins come crashing down when the virus effectively shuts off red cell production in the marrow.
Bile
Sterocobilin(ogen)
Faeces
Bacterial action
Urobilin(ogen)
Urine
Figure 1 Normal breakdown of haemoglobin. Excessive amounts of free haemoglobin overloads the above system which is taking place in the macrophages in the reticuloendothelial system and free haemoglobin enters the plasma directly resulting in haemoglobinaemia, haemoglobinuria.
Types of haemolysis (intravascular and extravascular) Normal, physiological haemolysis is low level and extravascular, via the RES. Abnormal, pathological haemolysis can be
robilin. The globin chains are degraded into amino acids, which u are reused in protein synthesis around the body.
Laboratory features of haemolysis
Abnormal haemolysis – haemolytic anaemia Lysis of RBCs is a normal daily process of removal of old cells, but if the lysis is accelerated and includes all RBCs, the destruction often outpaces the repopulation and anaemia develops; hence the term ‘haemolytic anaemia’. A sudden drop in haemoglobin/RBCs in the peripheral blood results in a massive surge in RBC production from the marrow, the first sign of which is seen in the peripheral blood, with an increase in the number of reticulocytes. The percentage of reticulocytes can increase dramatically, from 1–2% (absolute count 50–100×109/litre) to sometimes greater than 20–50%. Reticulocytes are larger than mature RBCS and on staining are bluer because of the RNA they contain; thus, a blood film is described as ‘polychromatic’ when there are many reticulocytes. The film might also be described as ‘dimorphic’, with two clear populations of cells – smaller red ones and larger, bluer ones. Examination of the bone marrow (which is rarely done at this point)
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Evidence of increased RBC breakdown • Raised bilirubin, largely unconjugated • Detectable/increased urobilinogen • Raised faecal stercobilinogen • Absent haptoglobins Evidence of increased RBC production • Reticulocytosis • Bone marrow erythroid hyperplasia Evidence of damaged RBCs • Morphological evidence (spherocytes, ‘bite cells’, Heinz bodies, ‘ghost cells’, haemoglobin puddling fragments) • Chromium-51-labelled RBC survival study (localization of haemolysis) Table 1
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Symposium: Haematology
extravascular or intravascular. It can also be intramedullary or extramedullary, occurring within or outside the bone marrow. Recognition of where the haemolysis is occurring gives clues to the probable cause. Causes of acute intravascular haemolysis are listed in Table 2.
Laboratory features of intravascular haemolysis • Haemoglobinaemia and haemoglobinuria • Haemosiderinuria • Methaemalbuminaemia
In intravascular haemolysis, RBCs are destroyed directly in the circulation, often rapidly. The haemoglobin from the lysed RBCs is released directly in to the plasma (haemoglobinaemia) and quickly saturates, forming complexes with, plasma haptoglobins (resulting in depleted haptoglobin levels). The complexes are removed by the RES, predominantly the liver. The remaining excess, unbound haemoglobin soon swamps the tubular resorptive capacity of the kidney and enters the urine (haemoglobinuria). The haemoglobin that is reabsorbed by the proximal tubules is broken down within the glomerular tubular cells. The iron from this breakdown is retained within the tubular cells and eventually excreted in the urine as haemosiderin. Haemosiderinuria is therefore a late sign of acute, or a sign of chronic, intravascular haemolysis. The haem and the globin are reabsorbed from the tubular cells into the plasma where the haem complexes with albumin forming methaemalbumin (methaemalbuminaemia) (Table 3). Massive and sudden intravascular haemolysis, as seen in ABO incompatibility and Blackwater fever (see below), can result in renal failure as lysed cells jam the circulation through the kidney.
NB: Urine may go dark on standing because of excess urobilinogen (as seen in extravascular haemolysis); that is, not due to the presence of haemoglobin. Need to exclude haematuria (whole RBCs due to bleeding in renal tract); hence, need for formal urinalysis, though dipstick analysis is helpful.
Table 3
Either RBCs are inherently faulty and unable to survive for any length of time (shortened lifespan) or they are normal, fully functional cells that come under attack and are destroyed prematurely. The former includes the inherited forms and the latter the acquired forms of haemolytic anaemia. Hereditary haemolytic anaemia: Effective erythropoiesis allows the production of normal quantities of normal RBCs resulting in a normal haemoglobin level. Ineffective erythropoiesis is the inefficient production of RBCs. The production, however, could be adequate, but the cells produced are poor-quality, dysfunctional cells that are destroyed and removed. Hereditary haemolytic anaemia can be divided in to three main groups: those with defects in the RBC membrane, RBC metabolism, or the synthesis of haemoglobin (Table 4). RBC membrane defects – a defect in the structure of the RBC membrane means that the cells cannot function as normal in the circulation. In the case of hereditary spherocytosis, the cells are spherocytic in shape and do not travel well through the spleen, often getting trapped and then destroyed. Hereditary spherocytosis is the most common hereditary haemolytic anaemia in Northern Europeans and most cases are inherited in an autosomal dominant manner. Patients have fluctuating jaundice and varying degrees of anaemia and most develop splenomegaly. Gallstones are often a problem. Patients are seen regularly in the clinic and assessed for their need for splenectomy (which is not necessary in every patient). They also require open-door access in case they develop an aplastic crisis (sudden onset of erythroblastopenia). Aplastic crisis is almost always due to parvovirus infection, which effectively wipes out the marked reticulocytosis that is so essential in sustaining these individuals’ baseline haemoglobin level. Patients present with sudden, profound anaemia, usually requiring transfusion unless there is rapid recovery of their reticulocyte count. Hereditary elliptocytosis is rarer and has a similar presentation. Defective RBC metabolism – a deficiency of any essential enzyme in the glycolytic pathway (pyruvate kinase) or hexose monophosphate shunt (glucose-6-phosphate dehydrogenase (G6PD) deficiency) renders the cell incapable of normal metabolism, and the death of the cell ensues. Deficiencies of any enzyme in either pathway can occur, but the two most common causing haemolytic anaemia are described below. • G6PD deficiency is the most common single-gene disorder worldwide, affecting more than 400 million people. It is an Xlinked condition, so suspicion should be raised in males from
In extravascular haemolysis, the cells are destroyed not in the circulation but by the organs of the RES – bone marrow, liver and spleen. Different types of extravascular haemolysis occur predominantly in one or all of these organs; for example, RBCs coated with IgG antibody tend to be destroyed by the spleen, whereas RBCs coated with complement and IgG tend to be removed more generally thoroughout the RES. Knowing this helps in deciding whether splenectomy would be of benefit to a patient with chronic haemolysis. Causes of haemolysis (hereditary and acquired) Knowing the consequences of where and possibly how the RBCs are being destroyed (intravascular or extravascular) is the first step in narrowing down the search for the cause of haemolysis.
Causes of acute intravascular haemolysis • Glucose-6-phosphate dehydrogenase deficiency with oxidant stress* • Drug- and infection-induced Malaria plus quinine (Blackwater fever*) • Autoimmune haemolytic anaemia (particularly cold forms) Paroxysmal cold haemoglobinuria* Cold agglutinins • Mismatched blood transfusioin* (ABO incompatibility) • RBC fragmentation (haemolytic uraemic syndrome) • Paroxysmal nocturnal haemoglobinuria *Often dramatic acute presentation.
Table 2
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Symposium: Haematology
Hereditary forms of haemolytic anaemia Category of defect
Clinical condition
Mechanism of defect
Molecular basis (mode of inheritance)
Haemoglobin synthesis
β-thalassaemia
Under- or absent production of β-globin chains Production of βS-globin chains and HbS Underproduction of α-globin genes Reduced synthesis of spectrin, unstable spectrin Abnormal spectrin dimer formation or spectrin–ankyrin association Reduced synthesis of enzyme, cannot generate NADPH Reduced synthesis of enzyme, reduced ATP formation
Mutations/deletions in β-globin gene (AR, occasionaly AD) Substitution of of valine for glutamic acid (sixth amino acid) (AR) Generally deletion of three of four α-globin genes (AR) Mutations involving spectrin synthesis (AD, occasionally AR) Mutations in α and β spectrin genes (AD and mild, but homozygous state occurs and causes severe haemolytic anaemia) Myriad mutations in G6PD gene (X-linked) Mutations in PK gene (AR)
Sickle cell disease α-thalassaemia/HbH disease Membrane
Hereditary spherocytosis Hereditary elliptocytosis
Enzyme
G6PD deficiency Pyruvate kinase deficiency
AR, autosomal recessive; AD, autosomal dominant; G6PD, glucose-6-phosphate dehydrogenase.
Table 4
the Mediterranean, Arab states and Asia (who have the more severe Western type B variant) and in Afro-Caribbeans, (who have the milder type A variant). G6PD also occurs occasionally in Caucasians. G6PD is essential for the generation of NADPH, which protects RBCs and haemoglobin against oxidative stress. Affected individuals are usually well and without jaundice or anaemia; haemolysis is intermittent and in many patients very occasional. However, oxidative stress due to infection, certain drugs (e.g. antimalarial agents, sulphonamides) or vitamin K, napththalene, henna or fava bean ingestion can result in sudden intravascular haemolysis. Many children have no further haemolytic episodes after neonatal jaundice and lead a normal life. Sudden onset of jaundice, associated with dark urine and then pallor (acute intravascular haemolysis), is the usual presentation in affected boys. Parents need to be aware of these signs, and children should have open-door access to a ward that knows how to manage such crises. • Pyruvate kinase deficiency is an autosomal recessive condition rarely seen in children outside Northern Europe/the Northern hemisphere. RBCs become rigid due to reduced ATP formation. Jaundice and anaemia are common, and in severe cases (those requiring regular transfusions) splenectomy helps. Gallstones are a common problem because of the constant haemolysis. Defects in haemoglobin synthesis – in β-thalassaemia there is little or absent production of β-globin chains, resulting in little or no HbA production. RBCs are made in the marrow but are so poorly haemoglobinized, mainly with HbF, that they are destroyed in the marrow (intramedullary haemolysis) as well as in the periphery (extramedullary haemolysis). Because of compensatory extramedullary haemopoiesis, and the removal of defective RBCs, both the liver and the spleen become enlarged. Hence, most haemoglobinopathies are haemolytic anaemias to a varying degree. Production of abnormal haemoglobins such as HbS and HbC causes sickle cell disease in the homozygote
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or compound heterozygote state. Deoxygenation of HbS causes sickling of RBCs and microvascular occlusion. This severe haemolytic disease is punctuated by crises, which can be painful vaso-occlusive, haemolytic, sequestration or aplastic in nature. There are numerous other, rarer haemoglobin variants that are unstable, haemolytic or both. Aplastic crises, almost always due to parvovirus infection, can occur in any immune-naive child with chronic haemolytic anaemia, and most devastatingly in those with marked haemolysis and high reticulocyte counts. Acquired forms of haemolytic anaemia can be divided in to two main groups: immune and non-immune. The immune forms can be auto- or alloimmune; the non-immune can be induced by drugs, chemicals, physical or infectious agents, or can be acquired e.g. paroxysmal nocturnal haemoglobinuria (Table 5). Autoimmune haemolytic anaemia (AIHA) – these anaemias are due to the production of autoantibodies, either warm (IgG), which bind RBCs most avidly at 37°C or cold (IgM), which bind RBCs most avidly at 4°C. The presence of antibody coated on RBCs results in a positive direct Coombs’ test (DCT). Warm AIHA is IgG positive with or without complement on the DCT and usually results in extravascular haemolysis. • The primary idiopathic form is in some cases related to drugs (e.g. methyldopa). • Secondary forms are rarer in young children as they are usually associated with underlying autoimmune disorders such as systemic lupus erythematosus, ulcerative colitis or rheumatoid arthritis in older patients. AIHA that occurs with idiopathic thrombocytopenic purpura (ITP) is called Evan’s syndrome. When cold antibodies (usually IgM, or rarely IgG) bind to RBCs, they do so in the peripheral circulation (fingers and toes) where the blood temperature is lower. Each antibody has different characteristics with different thermal amplitudes and 336
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negative. Jaundice is usually marked but the anaemia is generally mild. Florid spherocytosis and polychromasia (due to reticulocytosis) along with nucleated RBCs are seen on the blood film. • Rare paternal RBC antigens – when fetal cells are present in the maternal circulation, an immune response (with production of maternal IgG, which can cross the placenta) can result, especially if the antigens are particularly immunogenic. Clinical disease can ensue if the antibodies are particularly avid and/or lytic. Drug-induced immune haemolysis can be caused by a variety of mechanisms, including autoantibody against a drug–RBC membrane complex (penicillin) or deposition of complement via a drug–protein antibody complex (chlorpropamide). The haemo lysis usually resolves with the removal of the suspected candidate drug. If unexplained haemolysis occurs in a child and no other obvious cause can be identified, check the child’s drug history (and the parents’ drug history – they may have left tablets lying around the home). Non-immune haemolytic anaemia – RBC fragmentation is a well-recognized form of non-immune haemolysis, particularly haemolytic uraemic syndrome in the paediatric setting. Other microangiopathic anaemias, which by definition have visible RBC fragmentation on the blood film, include thrombotic thrombocytopenic purpura (ITP) and disseminated intravascular coagulation (DIC). Physical fragmentation of RBCs occurs with leaky artificial heart valves. • Septicaemia secondary to meningococcal, pneumococcal and Clostridium perfringens infection is a cause of fragmentation haemolysis and DIC. Blackwater fever is acute intravascular haemolysis in association with malaria, and malaria can also cause extravascular haemolysis. • Oxidative intravascular haemolysis can occur with high doses of drugs such as dapsone and salazopyrine. High levels of copper in Wilson’s disease, snake and spider bites, and burns also cause haemolysis. • Paroxysmal nocturnal haemoglobinuria is very rare in children and may be seen in association with severe aplastic anaemia. It is an acquired X-linked disorder of the PIGa genes essential for anchoring certain proteins that protect RBCs against lysis by complement. There is typically early morning haemoglobinuria, with lysis overnight as the pH declines during sleep. Marked haemosiderinuira can lead to iron deficiency. Thrombosis of the large vessels is a problem, particularly Budd–Chiari syndrome. • Congenital erythropoietic prophyria (Gunther’s disease) is a very rare form of porphyria. It causes haemolysis, severe photosensitivity with bullous eruptions and scarring, and red teeth.
Acquired forms of haemolytic anaemia Immune haemolytic anaemia • Autoimmune haemolytic anaemia (AIHA) Warm AIHA Cold AIHA Paroxysmal cold haemoglobinuria • Alloimmune haemolytic anaemia Rhesus disease of the newborn ABO incompatibility • Drug-induced immune Non-immune haemolytic anaemia • RBC fragmentation • Infections • Chemical and physical agents • Paroxysmal nocturnal haemoglobinuria and congenital erythropoietic prophyria (rare) Table 5
s pecificities. The antibody may detach from the RBCs as they pass into the warmer central circulation, but if complement has already bound to the surface of the RBCS it remains there and the DCT is positive, but for complement (C3d) only (and not IgM). Cold AIHA may be idiopathic or secondary. • Paroxysmal cold haemoglobinuria (PCH) is an important but rare cause of acute intravascular haemolysis in children. Its onset is sudden and dramatic (dark urine and jaundice followed by extreme pallor), but it is self-limiting and once haemolysis has occurred the child recovers completely, though blood transfusion is often required. The precipitant is usually a viral infection (varicella, measles, mumps), but PCH can occur after measles immunization. The antibody is unusually IgG and biphasic and is called the Donath–Landsteiner antibody. In the past, when syphilis was more prevalent/untreated, PCH was seen in adults. • Secondary cold AIHA is caused by an infection, particularly Mycoplasma, cytomegalovirus or Epstein–Barr virus (infectious mononucleosis), or an underlying lymphoproliferative disorder such as lymphoma. Alloimmune haemolytic anaemia – in the neonatal period, antibodies from the maternal circulation (IgG) enter the fetal circulation, and coat and destroy the fetal, and subsequently neonatal, RBCs. • Anti-D rhesus (haemolytic) disease of the newborn (HDN) used to be a major problem, but has become less so since the advent of prophylaxis with anti-D for rhesus-negative mothers. Antibodies against other rhesus antigens (c, C, E, e) can also cause HDN and now constitute most cases. Anaemia is generally more of a problem than jaundice. Maternal anti-Kell antibody can cause RBC aplasia rather than striking haemolysis, as destruction of more primitive cells occurs. • ABO incompatibility rarely causes marked clinical problems (only 1–2% of cases), despite the fact that 15% of pregnancies are ABO incompatible. The reason is that maternal IgG is required to cross the placenta (all mothers have passive IgM antibodies but few have sufficient levels of immune IgG antibodies) and antigens on fetal/neonatal RBCs are sparse. Thus, the DCT is sometimes
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Neonatal haemolysis Jaundice within the first 48 hours of life is pathological, and haematological causes could be any of those mentioned above. Of the hereditary forms, G6PD deficiency in male infants or hereditary spherocytosis should be considered. An important caveat is that most neonates have spherocytes in their peripheral blood, so it is best to delay confirmation of a diagnosis of hereditary spherocytosis until the baby is a few months old. There is a very rare variant of hereditary elliptocytosis called hereditary pyropoikilocytosis that causes striking haemolysis with an extremely bizarre blood picture (with a family history in about 30% of kindreds). Alloimmune haemolysis occurs predominantly in the neonatal period as described above, but autoimmune haemolysis is rare 337
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in neonates. There are other forms of neonatal haemolysis for which a cause is often not found, though most seem to be selflimiting. These include the folllowing. Heinz body haemolysis – evidence of haemolysis, predominantly ‘bite cells’, on the blood film should generate a search for Heniz bodies (denatured haemoglobin in RBC). Most cases are probably due to transient neonatal deficiency of protective enzymes/ substances such as catalase and vitamin E glutathione reductase. Infantile pyknocytosis is a rare and transient haemolytic anaemia, often with marked anaemia requiring blood transfusion. The blood film is characteristic but the cause is unknown.
Management of haemolytic anaemia • Seek advice from haematologist • Avoid transfusion of blood unless essential, especially in patients with immune haemolysis • ‘Masterly inactivity’ – careful clinical and laboratory monitoring of patient and blood picture may reveal that the haemolysis, though brisk and dramatic, has now ceased and that the child’s bone marrow and reticulocyte response will negate the need for blood (experienced clinical judgement required) • Give blood slowly, especially in patients with profound anaemia, heart failure or immune haemolysis • Warm blood safely and correctly using a properly functioning blood warmer in patients with cold AIHA • Treatment with prednisolone 2 mg/kg/day may be required in rampant warm (IgG) AIHA • Start folic acid 5 mg/day in children over 1 year (500 μg/kg/ day in the under-1s)
Investigating haemolysis The clinical history and presentation with relevant family and drug history give an immediate indication of the likely cause. Clinical examination including direct urinalysis will further advance the clinican’s suspicions. Table 6 lists the initial tests that should be performed in the investigation of haemolytic anaemia. More comprehensive and complex investigations should then be performed based on the results of the initial investigations.
AIHA, autoimmune haemolytic anaemia.
Table 7
Management of (acute) haemolysis
If, in extremis, a baby or child is profoundly anaemic and urgent transfusion of RBCs is considered life-saving, always ensure that appropriate bloods are taken before the transfusion is given. These include samples for the tests outlined in Table 6, along with at least one spare EDTA and clotted (serum) sample (for virology). If cold agglutination (suggestive of cold AIHA) is seen on the blood film or in the transfusion laboratory, warmed blood should be given, provided appropriate warming devices are available (radiators, armpits and microwaves are not to be used). Blood should be given slowly to any child with active immune haemolysis, preferably no faster than 5 ml/kg over a 3–4 hour period. Ideally, transfusion should be avoided unless absolutely necessary. Treatment for underlying infection, especially with Mycoplasma, should be started. Warm AIHA can respond to corticosteroids, and prednisolone 1–2 mg/kg/day may help in IgG-positive warm AHIA or severe mixed (warm and cold) AIHA. Most virus-induced AIHAs are cold and usually self-limiting, and do not generally respond to corticosteroid therapy. Folic acid 5 mg/day in children over 1 year (500 μg/kg/day in the under-1s) should be started and continued until haemolysis ceases and the haemoglobin is normal. Children with chronic haemolysis remain on folic acid lifelong. Children with chronic haemolytic anaemia are managed on an outpatient basis with regular 3–6-monthly review. They need lifelong folic acid and review for consideration of splenectomy. Parents of patients with G6PD deficiency must be educated about the possible precipitants, and the signs and symptoms, of an acute haemolytic crisis. The child should have open-door access so that an acute crisis can be managed appropriately. Often a crisis is mild, and blood tests and reassurance are all that is required. In more severe cases, the child may need close monitoring and assessment of whether the acute event is over and whether he or she can recover without a blood transfusion. ◆
Management of haemolytic anaemia depends on the cause, but a good rule is to do nothing until you know what you are treating and to enlist the specialist help of a haematologist as soon as possible (Table 7).
Investigation of haemolytic anaemia Initial • Full blood count with reticulocyte count • Blood film inspection • DCT • Serum bilirubin and lactate dehydrogenase, aspartate aminotransferase • Urine: colour inspection and dipstick More detailed, as required • Suspected cold agglutinins/cold autoimmune haemolytic anaemia: take warm DCT sample (get help and advice from laboratory) • Warm (37°C) sample for paroxysmal cold haemoglobinuria screen (seek specialist help) • Urine: haemosiderin and haemoglobin • Serum haptoglobins, screen for haemoglobinaemia • RBC enzyme assays: glucose-6-phosphate dehydrogenase, pyruvate kinase; if negative, may need to send blood to screen for rarer defects if an enzyme defect is thought likely • Suspected haemoglobin variant: haemoglobin electrophoresis or further, more complex investigations for unstable variants • In neonate: blood group of mother and infant and DCT of infant’s blood DCT, direct Coombs’ test.
Table 6
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Recommended reading Hoffbrand AV, Moss PAH, Petit JE. Essential haematology, 5th edn. Oxford: Blackwell, 2006. Smith H. Diagnosis in paediatric haematology. Edinburgh: Churchill Livingstone, 1996.
Practice points • Do not treat anaemia until you know what you are treating • The few causes of acute haemolysis should be known to all paediatricians; most are acquired, either immune or nonimmune, except G6PD deficiency • Hereditary haemolytic anaemias have a chronic course or one punctuated by acute crises • The reticulocyte count and inspection of the peripheral blood are essential in any investigation into anaemia, but are particularly useful in children with haemolysis • Always seek the help and advice of a haematologist, particularly for the interpretation of laboratory data and patient management if in any doubt
Further reading Eyssette-Guerreau S, Bader-Meunier B, Garcon L, et al. Infantile pyknocytosis: a cause of haemolytic anaemia of the newborn. Br J Haematol 2006; 133: 439–42. Lewis SM, Bain BJ, Bates I. Dacie and Lewis practical haematology, 10th edn. Edinburgh: Churchill Livingstone, 2006. Murphy MF, Pamphilon DH. Practical transfusion medicine. Oxford: Blackwells, 2001.
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Understanding haemolytic anaemia
Haemolysis Lysis of RBCs is part of the daily physiological process of RBC turnover. However, the term ‘haemolysis’ is used when referring to the accelerated, pathological forms of haemolysis that result in anaemia and jaundice.
Georgina W Hall
Normal haemolysis Maintaining normal haemoglobin levels – the role of the reticulocyte: RBC production (erythropoiesis) involves a constant turnover of cells. Normally, effete red cells are lysed at the end of their life by macrophages in the reticuloendothelial system (RES) mainly in the bone marrow but also in the liver and spleen. This process is known as extravascular haemolysis; that is, the lysis does not occur intravascularly in the blood vessels. The normal lifespan of an RBC is 100–120 days. This process of natural wastage is controlled and balanced. As an old cell is removed, a new RBC, the reticulocyte, recently rid of its nucleus but still replete with RNA and synthetic abilities, appears in the blood fresh from the bone marrow ready to spend the next 100 days or so working in the peripheral blood. Normally, 1–2% of circulating RBCs are reticulocytes, and this small proportion is all that is required to maintain a normal haemoglobin level in the steady state. The reason why anaemia does not occur normally is that there is a balance between destruction and repopulation that is controlled by various physiological mechanisms (oxygen sensors and production of erythropoietin (Epo) in the kidney).
Abstract Understanding haemolytic anaemia means understanding the pathophysiology of accelerated red blood cell (RBC) lysis. Clinicians need to be aware of the different types of haemolysis, intravascular and extravascular, and the causes, both inherited and acquired. Appreciation of these facts will ensure that appropriate first-line investigations are performed in jaundiced anaemic children when they first present. Specialist advice should then be obtained to ensure the best management of these children. Acute and often self-limiting forms of haemolysis can be the most dramatic and these are the forms most likely to present to the general paediatrician.
Keywords haemolysis; hereditary and acquired; immune and non-immune haemolytic anaemia; intravascular and extravascular; haemoglobinuria; reticulocytosis
Physiology of RBC production: In the bone marrow, stem cell progenitors with Epo receptors become committed to erythropoiesis. This commitment is increased (i.e. more progenitors are pushed into RBC production as opposed to making white blood cells (WBCs) or platelets) when there are higher levels of circulating Epo (analogous to car production in factory when there is an increased demand for red cars). Increased production of Epo from the kidney occurs when the oxygen tension in the kidney, for whatever reason, declines. These committed progenitors differentiate and grow through the various stages of development (pro-normoblast to normo(erythro)blasts – early, intermediate and late) until they eject their nucleus and become reticulocytes.
Introduction Understanding haemolytic anaemias requires a knowledge of both the physiology of red blood cell (RBC) production and breakdown, and the pathophysiology of haemolysis. Clinicians who understand haemolysis can investigate, intelligently a jaundiced, anaemic child. Most paediatricians see cases of haemolysis during their time on the neonatal unit and while doing acute on-call for paediatrics. However, most children with chronic or hereditary forms of haemolysis are under specialist care, often with open-door access, and are therefore seen predominantly by those working in haematology units rather than by general paediatricians. After reacquainting the clinician with basic RBC physiology and the pathophysiology of RBC lysis, this review discusses the various types and causes of haemolysis, both hereditary and acquired. More detailed information can be obtained from the recommended Further Reading. Management of a jaundiced/ anaemic child depends on the underlying cause. The presentation, ethnic origin and family history of each patient should lead to a suspicion of the most likely diagnosis and hence the appropriate investigations. The advice and support of a haematologist should always be sought, and in difficult cases the (paediatric) haematologist should be the lead for the care of the child.
Physiology of RBC breakdown: The breakdown of an RBC is in part a recycling process (Figure 1), and understanding this physiological process makes understanding haemolysis easy. The haemoglobin is broken down into haem and globin. The haem is broken down into iron, which is bound and transferred by transferrin to the marrow erythroblasts (primitive RBCs growing in the bone marrow) and protoporphyrin, which is broken down mainly into bilirubin with some carbon monoxide (which is expired via the lungs). Remembering what happens to the bilirubin is essential in understanding how to investigate haemolysis. Bilirubin is normally circulated to the liver where it is conjugated to bilirubin glucuronides, which are excreted into the gut via the bile and converted to stercobilionogen and stercobilin, which are excreted in the faeces. Some stercobiliogen and stercobilin is reabsorbed and excreted in the urine as urobilinogen and
Georgina W Hall PhD FRCP FRCPath FRCPCH is Consultant Paediatric Haematologist at the Department of Paediatric Haematology/Oncology, Oxford Children’s Hospital, Headington, Oxford OX3 9DU, UK.
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would reveal marked erythroid hyperplasia; that is, a massive increase in RBC production. In acute and profound anaemia, nucleated RBCs (late normoblasts; the stage just before reticulocytes, normally only seen in the peripheral blood of neonates and in the bone marrow of everyone else) also appear in the peripheral blood. The result of this massive surge in activity is to bring the haemoglobin level back to normal, at which point the marrow and reticulocyte count can settle back down to normal activity, provided the destructive process has ceased. Note that in some very acute forms of brisk haemolysis, there is often a delay in the reticulocyte response and confusion may arise as to whether the anaemia is reticulocytopenic, as may be seen in transient erythroblastopenia of childhood (TEC), or even Diamond Blackfan anaemia (DBA). However, obvious signs of haemolysis, if they are still present, usually allay such fears (Table 1).
Haemoglobin
Haem
Globin
Protoporphyrin
Iron
Amino acids
Bilirubin (free)
CO
Transferrin
Liver
Bilirubin glucuronides
Bone marrow
Red cell precursors: Erythroblasts
Compensated haemolysis Depending on the degree or chronicity of the process, haemolytic anaemia can be compensated; that is, the reticulocyte response is such that the haemoglobin is maintained within the normal range and the patient is not anaemic (though he or she may be jaundiced) despite ongoing haemolysis. A normal marrow, working effectively and producing normal RBCs can produce cells at 6–8 times the normal rate in the face of increased destruction. Patients with ineffective erythropoiesis (whose marrows are unable to make normal cells) cannot mount such a response and often become profoundly anaemic quite dramatically. An example of this is a parvovirus-induced aplastic crisis in a patient with a chronic haemolytic anaemia such as hereditary spherocytosis (HS) or sickle cell disease). In these patients, so dependent on a high reticulocyte count, their haemoglobins come crashing down when the virus effectively shuts off red cell production in the marrow.
Bile
Sterocobilin(ogen)
Faeces
Bacterial action
Urobilin(ogen)
Urine
Figure 1 Normal breakdown of haemoglobin. Excessive amounts of free haemoglobin overloads the above system which is taking place in the macrophages in the reticuloendothelial system and free haemoglobin enters the plasma directly resulting in haemoglobinaemia, haemoglobinuria.
Types of haemolysis (intravascular and extravascular) Normal, physiological haemolysis is low level and extravascular, via the RES. Abnormal, pathological haemolysis can be
robilin. The globin chains are degraded into amino acids, which u are reused in protein synthesis around the body.
Laboratory features of haemolysis
Abnormal haemolysis – haemolytic anaemia Lysis of RBCs is a normal daily process of removal of old cells, but if the lysis is accelerated and includes all RBCs, the destruction often outpaces the repopulation and anaemia develops; hence the term ‘haemolytic anaemia’. A sudden drop in haemoglobin/RBCs in the peripheral blood results in a massive surge in RBC production from the marrow, the first sign of which is seen in the peripheral blood, with an increase in the number of reticulocytes. The percentage of reticulocytes can increase dramatically, from 1–2% (absolute count 50–100×109/litre) to sometimes greater than 20–50%. Reticulocytes are larger than mature RBCS and on staining are bluer because of the RNA they contain; thus, a blood film is described as ‘polychromatic’ when there are many reticulocytes. The film might also be described as ‘dimorphic’, with two clear populations of cells – smaller red ones and larger, bluer ones. Examination of the bone marrow (which is rarely done at this point)
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Evidence of increased RBC breakdown • Raised bilirubin, largely unconjugated • Detectable/increased urobilinogen • Raised faecal stercobilinogen • Absent haptoglobins Evidence of increased RBC production • Reticulocytosis • Bone marrow erythroid hyperplasia Evidence of damaged RBCs • Morphological evidence (spherocytes, ‘bite cells’, Heinz bodies, ‘ghost cells’, haemoglobin puddling fragments) • Chromium-51-labelled RBC survival study (localization of haemolysis) Table 1
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extravascular or intravascular. It can also be intramedullary or extramedullary, occurring within or outside the bone marrow. Recognition of where the haemolysis is occurring gives clues to the probable cause. Causes of acute intravascular haemolysis are listed in Table 2.
Laboratory features of intravascular haemolysis • Haemoglobinaemia and haemoglobinuria • Haemosiderinuria • Methaemalbuminaemia
In intravascular haemolysis, RBCs are destroyed directly in the circulation, often rapidly. The haemoglobin from the lysed RBCs is released directly in to the plasma (haemoglobinaemia) and quickly saturates, forming complexes with, plasma haptoglobins (resulting in depleted haptoglobin levels). The complexes are removed by the RES, predominantly the liver. The remaining excess, unbound haemoglobin soon swamps the tubular resorptive capacity of the kidney and enters the urine (haemoglobinuria). The haemoglobin that is reabsorbed by the proximal tubules is broken down within the glomerular tubular cells. The iron from this breakdown is retained within the tubular cells and eventually excreted in the urine as haemosiderin. Haemosiderinuria is therefore a late sign of acute, or a sign of chronic, intravascular haemolysis. The haem and the globin are reabsorbed from the tubular cells into the plasma where the haem complexes with albumin forming methaemalbumin (methaemalbuminaemia) (Table 3). Massive and sudden intravascular haemolysis, as seen in ABO incompatibility and Blackwater fever (see below), can result in renal failure as lysed cells jam the circulation through the kidney.
NB: Urine may go dark on standing because of excess urobilinogen (as seen in extravascular haemolysis); that is, not due to the presence of haemoglobin. Need to exclude haematuria (whole RBCs due to bleeding in renal tract); hence, need for formal urinalysis, though dipstick analysis is helpful.
Table 3
Either RBCs are inherently faulty and unable to survive for any length of time (shortened lifespan) or they are normal, fully functional cells that come under attack and are destroyed prematurely. The former includes the inherited forms and the latter the acquired forms of haemolytic anaemia. Hereditary haemolytic anaemia: Effective erythropoiesis allows the production of normal quantities of normal RBCs resulting in a normal haemoglobin level. Ineffective erythropoiesis is the inefficient production of RBCs. The production, however, could be adequate, but the cells produced are poor-quality, dysfunctional cells that are destroyed and removed. Hereditary haemolytic anaemia can be divided in to three main groups: those with defects in the RBC membrane, RBC metabolism, or the synthesis of haemoglobin (Table 4). RBC membrane defects – a defect in the structure of the RBC membrane means that the cells cannot function as normal in the circulation. In the case of hereditary spherocytosis, the cells are spherocytic in shape and do not travel well through the spleen, often getting trapped and then destroyed. Hereditary spherocytosis is the most common hereditary haemolytic anaemia in Northern Europeans and most cases are inherited in an autosomal dominant manner. Patients have fluctuating jaundice and varying degrees of anaemia and most develop splenomegaly. Gallstones are often a problem. Patients are seen regularly in the clinic and assessed for their need for splenectomy (which is not necessary in every patient). They also require open-door access in case they develop an aplastic crisis (sudden onset of erythroblastopenia). Aplastic crisis is almost always due to parvovirus infection, which effectively wipes out the marked reticulocytosis that is so essential in sustaining these individuals’ baseline haemoglobin level. Patients present with sudden, profound anaemia, usually requiring transfusion unless there is rapid recovery of their reticulocyte count. Hereditary elliptocytosis is rarer and has a similar presentation. Defective RBC metabolism – a deficiency of any essential enzyme in the glycolytic pathway (pyruvate kinase) or hexose monophosphate shunt (glucose-6-phosphate dehydrogenase (G6PD) deficiency) renders the cell incapable of normal metabolism, and the death of the cell ensues. Deficiencies of any enzyme in either pathway can occur, but the two most common causing haemolytic anaemia are described below. • G6PD deficiency is the most common single-gene disorder worldwide, affecting more than 400 million people. It is an Xlinked condition, so suspicion should be raised in males from
In extravascular haemolysis, the cells are destroyed not in the circulation but by the organs of the RES – bone marrow, liver and spleen. Different types of extravascular haemolysis occur predominantly in one or all of these organs; for example, RBCs coated with IgG antibody tend to be destroyed by the spleen, whereas RBCs coated with complement and IgG tend to be removed more generally thoroughout the RES. Knowing this helps in deciding whether splenectomy would be of benefit to a patient with chronic haemolysis. Causes of haemolysis (hereditary and acquired) Knowing the consequences of where and possibly how the RBCs are being destroyed (intravascular or extravascular) is the first step in narrowing down the search for the cause of haemolysis.
Causes of acute intravascular haemolysis • Glucose-6-phosphate dehydrogenase deficiency with oxidant stress* • Drug- and infection-induced Malaria plus quinine (Blackwater fever*) • Autoimmune haemolytic anaemia (particularly cold forms) Paroxysmal cold haemoglobinuria* Cold agglutinins • Mismatched blood transfusioin* (ABO incompatibility) • RBC fragmentation (haemolytic uraemic syndrome) • Paroxysmal nocturnal haemoglobinuria *Often dramatic acute presentation.
Table 2
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Hereditary forms of haemolytic anaemia Category of defect
Clinical condition
Mechanism of defect
Molecular basis (mode of inheritance)
Haemoglobin synthesis
β-thalassaemia
Under- or absent production of β-globin chains Production of βS-globin chains and HbS Underproduction of α-globin genes Reduced synthesis of spectrin, unstable spectrin Abnormal spectrin dimer formation or spectrin–ankyrin association Reduced synthesis of enzyme, cannot generate NADPH Reduced synthesis of enzyme, reduced ATP formation
Mutations/deletions in β-globin gene (AR, occasionaly AD) Substitution of of valine for glutamic acid (sixth amino acid) (AR) Generally deletion of three of four α-globin genes (AR) Mutations involving spectrin synthesis (AD, occasionally AR) Mutations in α and β spectrin genes (AD and mild, but homozygous state occurs and causes severe haemolytic anaemia) Myriad mutations in G6PD gene (X-linked) Mutations in PK gene (AR)
Sickle cell disease α-thalassaemia/HbH disease Membrane
Hereditary spherocytosis Hereditary elliptocytosis
Enzyme
G6PD deficiency Pyruvate kinase deficiency
AR, autosomal recessive; AD, autosomal dominant; G6PD, glucose-6-phosphate dehydrogenase.
Table 4
the Mediterranean, Arab states and Asia (who have the more severe Western type B variant) and in Afro-Caribbeans, (who have the milder type A variant). G6PD also occurs occasionally in Caucasians. G6PD is essential for the generation of NADPH, which protects RBCs and haemoglobin against oxidative stress. Affected individuals are usually well and without jaundice or anaemia; haemolysis is intermittent and in many patients very occasional. However, oxidative stress due to infection, certain drugs (e.g. antimalarial agents, sulphonamides) or vitamin K, napththalene, henna or fava bean ingestion can result in sudden intravascular haemolysis. Many children have no further haemolytic episodes after neonatal jaundice and lead a normal life. Sudden onset of jaundice, associated with dark urine and then pallor (acute intravascular haemolysis), is the usual presentation in affected boys. Parents need to be aware of these signs, and children should have open-door access to a ward that knows how to manage such crises. • Pyruvate kinase deficiency is an autosomal recessive condition rarely seen in children outside Northern Europe/the Northern hemisphere. RBCs become rigid due to reduced ATP formation. Jaundice and anaemia are common, and in severe cases (those requiring regular transfusions) splenectomy helps. Gallstones are a common problem because of the constant haemolysis. Defects in haemoglobin synthesis – in β-thalassaemia there is little or absent production of β-globin chains, resulting in little or no HbA production. RBCs are made in the marrow but are so poorly haemoglobinized, mainly with HbF, that they are destroyed in the marrow (intramedullary haemolysis) as well as in the periphery (extramedullary haemolysis). Because of compensatory extramedullary haemopoiesis, and the removal of defective RBCs, both the liver and the spleen become enlarged. Hence, most haemoglobinopathies are haemolytic anaemias to a varying degree. Production of abnormal haemoglobins such as HbS and HbC causes sickle cell disease in the homozygote
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or compound heterozygote state. Deoxygenation of HbS causes sickling of RBCs and microvascular occlusion. This severe haemolytic disease is punctuated by crises, which can be painful vaso-occlusive, haemolytic, sequestration or aplastic in nature. There are numerous other, rarer haemoglobin variants that are unstable, haemolytic or both. Aplastic crises, almost always due to parvovirus infection, can occur in any immune-naive child with chronic haemolytic anaemia, and most devastatingly in those with marked haemolysis and high reticulocyte counts. Acquired forms of haemolytic anaemia can be divided in to two main groups: immune and non-immune. The immune forms can be auto- or alloimmune; the non-immune can be induced by drugs, chemicals, physical or infectious agents, or can be acquired e.g. paroxysmal nocturnal haemoglobinuria (Table 5). Autoimmune haemolytic anaemia (AIHA) – these anaemias are due to the production of autoantibodies, either warm (IgG), which bind RBCs most avidly at 37°C or cold (IgM), which bind RBCs most avidly at 4°C. The presence of antibody coated on RBCs results in a positive direct Coombs’ test (DCT). Warm AIHA is IgG positive with or without complement on the DCT and usually results in extravascular haemolysis. • The primary idiopathic form is in some cases related to drugs (e.g. methyldopa). • Secondary forms are rarer in young children as they are usually associated with underlying autoimmune disorders such as systemic lupus erythematosus, ulcerative colitis or rheumatoid arthritis in older patients. AIHA that occurs with idiopathic thrombocytopenic purpura (ITP) is called Evan’s syndrome. When cold antibodies (usually IgM, or rarely IgG) bind to RBCs, they do so in the peripheral circulation (fingers and toes) where the blood temperature is lower. Each antibody has different characteristics with different thermal amplitudes and 336
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negative. Jaundice is usually marked but the anaemia is generally mild. Florid spherocytosis and polychromasia (due to reticulocytosis) along with nucleated RBCs are seen on the blood film. • Rare paternal RBC antigens – when fetal cells are present in the maternal circulation, an immune response (with production of maternal IgG, which can cross the placenta) can result, especially if the antigens are particularly immunogenic. Clinical disease can ensue if the antibodies are particularly avid and/or lytic. Drug-induced immune haemolysis can be caused by a variety of mechanisms, including autoantibody against a drug–RBC membrane complex (penicillin) or deposition of complement via a drug–protein antibody complex (chlorpropamide). The haemo lysis usually resolves with the removal of the suspected candidate drug. If unexplained haemolysis occurs in a child and no other obvious cause can be identified, check the child’s drug history (and the parents’ drug history – they may have left tablets lying around the home). Non-immune haemolytic anaemia – RBC fragmentation is a well-recognized form of non-immune haemolysis, particularly haemolytic uraemic syndrome in the paediatric setting. Other microangiopathic anaemias, which by definition have visible RBC fragmentation on the blood film, include thrombotic thrombocytopenic purpura (ITP) and disseminated intravascular coagulation (DIC). Physical fragmentation of RBCs occurs with leaky artificial heart valves. • Septicaemia secondary to meningococcal, pneumococcal and Clostridium perfringens infection is a cause of fragmentation haemolysis and DIC. Blackwater fever is acute intravascular haemolysis in association with malaria, and malaria can also cause extravascular haemolysis. • Oxidative intravascular haemolysis can occur with high doses of drugs such as dapsone and salazopyrine. High levels of copper in Wilson’s disease, snake and spider bites, and burns also cause haemolysis. • Paroxysmal nocturnal haemoglobinuria is very rare in children and may be seen in association with severe aplastic anaemia. It is an acquired X-linked disorder of the PIGa genes essential for anchoring certain proteins that protect RBCs against lysis by complement. There is typically early morning haemoglobinuria, with lysis overnight as the pH declines during sleep. Marked haemosiderinuira can lead to iron deficiency. Thrombosis of the large vessels is a problem, particularly Budd–Chiari syndrome. • Congenital erythropoietic prophyria (Gunther’s disease) is a very rare form of porphyria. It causes haemolysis, severe photosensitivity with bullous eruptions and scarring, and red teeth.
Acquired forms of haemolytic anaemia Immune haemolytic anaemia • Autoimmune haemolytic anaemia (AIHA) Warm AIHA Cold AIHA Paroxysmal cold haemoglobinuria • Alloimmune haemolytic anaemia Rhesus disease of the newborn ABO incompatibility • Drug-induced immune Non-immune haemolytic anaemia • RBC fragmentation • Infections • Chemical and physical agents • Paroxysmal nocturnal haemoglobinuria and congenital erythropoietic prophyria (rare) Table 5
s pecificities. The antibody may detach from the RBCs as they pass into the warmer central circulation, but if complement has already bound to the surface of the RBCS it remains there and the DCT is positive, but for complement (C3d) only (and not IgM). Cold AIHA may be idiopathic or secondary. • Paroxysmal cold haemoglobinuria (PCH) is an important but rare cause of acute intravascular haemolysis in children. Its onset is sudden and dramatic (dark urine and jaundice followed by extreme pallor), but it is self-limiting and once haemolysis has occurred the child recovers completely, though blood transfusion is often required. The precipitant is usually a viral infection (varicella, measles, mumps), but PCH can occur after measles immunization. The antibody is unusually IgG and biphasic and is called the Donath–Landsteiner antibody. In the past, when syphilis was more prevalent/untreated, PCH was seen in adults. • Secondary cold AIHA is caused by an infection, particularly Mycoplasma, cytomegalovirus or Epstein–Barr virus (infectious mononucleosis), or an underlying lymphoproliferative disorder such as lymphoma. Alloimmune haemolytic anaemia – in the neonatal period, antibodies from the maternal circulation (IgG) enter the fetal circulation, and coat and destroy the fetal, and subsequently neonatal, RBCs. • Anti-D rhesus (haemolytic) disease of the newborn (HDN) used to be a major problem, but has become less so since the advent of prophylaxis with anti-D for rhesus-negative mothers. Antibodies against other rhesus antigens (c, C, E, e) can also cause HDN and now constitute most cases. Anaemia is generally more of a problem than jaundice. Maternal anti-Kell antibody can cause RBC aplasia rather than striking haemolysis, as destruction of more primitive cells occurs. • ABO incompatibility rarely causes marked clinical problems (only 1–2% of cases), despite the fact that 15% of pregnancies are ABO incompatible. The reason is that maternal IgG is required to cross the placenta (all mothers have passive IgM antibodies but few have sufficient levels of immune IgG antibodies) and antigens on fetal/neonatal RBCs are sparse. Thus, the DCT is sometimes
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Neonatal haemolysis Jaundice within the first 48 hours of life is pathological, and haematological causes could be any of those mentioned above. Of the hereditary forms, G6PD deficiency in male infants or hereditary spherocytosis should be considered. An important caveat is that most neonates have spherocytes in their peripheral blood, so it is best to delay confirmation of a diagnosis of hereditary spherocytosis until the baby is a few months old. There is a very rare variant of hereditary elliptocytosis called hereditary pyropoikilocytosis that causes striking haemolysis with an extremely bizarre blood picture (with a family history in about 30% of kindreds). Alloimmune haemolysis occurs predominantly in the neonatal period as described above, but autoimmune haemolysis is rare 337
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in neonates. There are other forms of neonatal haemolysis for which a cause is often not found, though most seem to be selflimiting. These include the folllowing. Heinz body haemolysis – evidence of haemolysis, predominantly ‘bite cells’, on the blood film should generate a search for Heniz bodies (denatured haemoglobin in RBC). Most cases are probably due to transient neonatal deficiency of protective enzymes/ substances such as catalase and vitamin E glutathione reductase. Infantile pyknocytosis is a rare and transient haemolytic anaemia, often with marked anaemia requiring blood transfusion. The blood film is characteristic but the cause is unknown.
Management of haemolytic anaemia • Seek advice from haematologist • Avoid transfusion of blood unless essential, especially in patients with immune haemolysis • ‘Masterly inactivity’ – careful clinical and laboratory monitoring of patient and blood picture may reveal that the haemolysis, though brisk and dramatic, has now ceased and that the child’s bone marrow and reticulocyte response will negate the need for blood (experienced clinical judgement required) • Give blood slowly, especially in patients with profound anaemia, heart failure or immune haemolysis • Warm blood safely and correctly using a properly functioning blood warmer in patients with cold AIHA • Treatment with prednisolone 2 mg/kg/day may be required in rampant warm (IgG) AIHA • Start folic acid 5 mg/day in children over 1 year (500 μg/kg/ day in the under-1s)
Investigating haemolysis The clinical history and presentation with relevant family and drug history give an immediate indication of the likely cause. Clinical examination including direct urinalysis will further advance the clinican’s suspicions. Table 6 lists the initial tests that should be performed in the investigation of haemolytic anaemia. More comprehensive and complex investigations should then be performed based on the results of the initial investigations.
AIHA, autoimmune haemolytic anaemia.
Table 7
Management of (acute) haemolysis
If, in extremis, a baby or child is profoundly anaemic and urgent transfusion of RBCs is considered life-saving, always ensure that appropriate bloods are taken before the transfusion is given. These include samples for the tests outlined in Table 6, along with at least one spare EDTA and clotted (serum) sample (for virology). If cold agglutination (suggestive of cold AIHA) is seen on the blood film or in the transfusion laboratory, warmed blood should be given, provided appropriate warming devices are available (radiators, armpits and microwaves are not to be used). Blood should be given slowly to any child with active immune haemolysis, preferably no faster than 5 ml/kg over a 3–4 hour period. Ideally, transfusion should be avoided unless absolutely necessary. Treatment for underlying infection, especially with Mycoplasma, should be started. Warm AIHA can respond to corticosteroids, and prednisolone 1–2 mg/kg/day may help in IgG-positive warm AHIA or severe mixed (warm and cold) AIHA. Most virus-induced AIHAs are cold and usually self-limiting, and do not generally respond to corticosteroid therapy. Folic acid 5 mg/day in children over 1 year (500 μg/kg/day in the under-1s) should be started and continued until haemolysis ceases and the haemoglobin is normal. Children with chronic haemolysis remain on folic acid lifelong. Children with chronic haemolytic anaemia are managed on an outpatient basis with regular 3–6-monthly review. They need lifelong folic acid and review for consideration of splenectomy. Parents of patients with G6PD deficiency must be educated about the possible precipitants, and the signs and symptoms, of an acute haemolytic crisis. The child should have open-door access so that an acute crisis can be managed appropriately. Often a crisis is mild, and blood tests and reassurance are all that is required. In more severe cases, the child may need close monitoring and assessment of whether the acute event is over and whether he or she can recover without a blood transfusion. ◆
Management of haemolytic anaemia depends on the cause, but a good rule is to do nothing until you know what you are treating and to enlist the specialist help of a haematologist as soon as possible (Table 7).
Investigation of haemolytic anaemia Initial • Full blood count with reticulocyte count • Blood film inspection • DCT • Serum bilirubin and lactate dehydrogenase, aspartate aminotransferase • Urine: colour inspection and dipstick More detailed, as required • Suspected cold agglutinins/cold autoimmune haemolytic anaemia: take warm DCT sample (get help and advice from laboratory) • Warm (37°C) sample for paroxysmal cold haemoglobinuria screen (seek specialist help) • Urine: haemosiderin and haemoglobin • Serum haptoglobins, screen for haemoglobinaemia • RBC enzyme assays: glucose-6-phosphate dehydrogenase, pyruvate kinase; if negative, may need to send blood to screen for rarer defects if an enzyme defect is thought likely • Suspected haemoglobin variant: haemoglobin electrophoresis or further, more complex investigations for unstable variants • In neonate: blood group of mother and infant and DCT of infant’s blood DCT, direct Coombs’ test.
Table 6
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Recommended reading Hoffbrand AV, Moss PAH, Petit JE. Essential haematology, 5th edn. Oxford: Blackwell, 2006. Smith H. Diagnosis in paediatric haematology. Edinburgh: Churchill Livingstone, 1996.
Practice points • Do not treat anaemia until you know what you are treating • The few causes of acute haemolysis should be known to all paediatricians; most are acquired, either immune or nonimmune, except G6PD deficiency • Hereditary haemolytic anaemias have a chronic course or one punctuated by acute crises • The reticulocyte count and inspection of the peripheral blood are essential in any investigation into anaemia, but are particularly useful in children with haemolysis • Always seek the help and advice of a haematologist, particularly for the interpretation of laboratory data and patient management if in any doubt
Further reading Eyssette-Guerreau S, Bader-Meunier B, Garcon L, et al. Infantile pyknocytosis: a cause of haemolytic anaemia of the newborn. Br J Haematol 2006; 133: 439–42. Lewis SM, Bain BJ, Bates I. Dacie and Lewis practical haematology, 10th edn. Edinburgh: Churchill Livingstone, 2006. Murphy MF, Pamphilon DH. Practical transfusion medicine. Oxford: Blackwells, 2001.
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