Hemolytic anemia

hemolytic anemia classification and pathogenesis

1. Hemolytic anemia Dr utsav parmar

2. Definition and Classification Anaemias resulting from an increase in the rate of red cell destruction. Normally, red cells undergo lysis at the end of their lifespan of 120±30 days within the cells of reticuloendothelial (RE) system in the spleen and elsewhere ( extravascular haemolysis ), and haemoglobin is not liberated into the plasma in appreciable amounts. The red cell lifespan is shortened in haemolytic anaemia i.e. there is accelerated haemolysis . However, shortening of red cell lifespan does not necessarily result in anaemia. In fact, compensatory bone marrow hyperplasia may cause 6 to 8-fold increase in red cell production without causing anaemia to the patient, so-called compensated haemolytic disease.

3. The premature destruction of red cells in haemolytic anaemia may occur by 2 mechanisms: Firstly, the red cells undergo lysis in the circulation and release their contents into plasma (intravascular haemolysis ). In these cases the plasma haemoglobin rises substantially and part of it may be excreted in the urine ( haemoglobinuria ). Secondly, the red cells are taken up by cells of the RE system where they are destroyed and digested ( extravascular haemolysis ). In extravascular haemolysis, plasma haemoglobin level is, therefore, barely raised .

4. Extravascular haemolysis is more common than the former. Haemolytic anaemias are broadly classified into 2 main categories: I. Acquired haemolytic anaemias caused by a variety of extrinsic environmental factors ( extracorpuscular ). II. Hereditary haemolytic anaemias are usually the result of intrinsic red cell defects ( intracorpuscular ). .

5. Classification of Haemolytic Anaemias I. ACQUIRED (EXTRACORPUSCULAR) A. Antibody: Immunohaemolytic anaemias 1. Autoimmune haemolytic anaemia (AIHA) i ) Warm antibody AIHA ii) Cold antibody AIHA 2. Drug-induced immunohaemolytic anaemia 3. Isoimmune haemolytic anaemia B. Mechanical trauma: Microangiopathic haemolytic anaemia C . Direct toxic effects: Malaria, bacterial, infection and other agents D. Acquired red cell membrane abnormalities: paroxysmal nocturnal haemoglobinuria (PNH) E. Splenomegaly

6. II. HEREDITARY (INTRACORPUSCULAR) A. Abnormalities of red cell membrane 1. Hereditary spherocytosis 2. Hereditary elliptocytosis (hereditary ovalocytosis ) 3. Hereditary stomatocytosis B. Disorders of red cell interior 1. Red cell enzyme defects ( Enzymopathies ) i ) Defects in the hexose monophosphate shunt: G6PD deficiency ii) Defects in the Embden -Meyerhof (or glycolytic ) pathway: pyruvate kinase deficiency 2. Disorders of haemoglobin ( Haemoglobinopathies ) i ) Structurally abnormal haemoglobins : sickle syndromes, other haemoglobinopathies ii) Reduced globin chain synthesis: thalassaemias

7. Features of Haemolysis GENERAL CLINICAL FEATURES 1. Presence of pallor of mucous membranes. 2. Positive family history with life-long anaemia in patients with congenital haemolytic anaemia. 3. Mild fluctuating jaundice due to unconjugated hyperbilirubinaemia . 4. Urine turns dark on standing due to excess of urobilinogen in urine. 5. Splenomegaly is found in most chronic haemolytic anaemias , both congenital and acquired. 6. Pigment gallstones are found in some cases.

8. LABORATORY EVALUATION OF HAEMOLYSIS 1. Is there evidence of haemolysis ? 2. What is the type of haemolytic mechanism? 3. What is the precise diagnosis? findings are conveniently divided into the following 4 groups:

9. I. Tests of increased red cell breakdown 1. Serum bilirubin —unconjugated (indirect) bilirubin is raised . 2 . Urine urobilinogen is raised but there is no bilirubinuria . 3. Faecal stercobilinogen is raised. 4. Serum haptoglobin (α-globulin binding protein) is reduced or absent . 5. Plasma lactic dehydrogenase (LDH) is raised. 6. Evidences of intravascular haemolysis in the form of haemoglobinaemia , haemoglobinuria , methaemoglobinaemia and haemosiderinuria .

10. II. Tests of increased red cell production 1. Reticulocyte count reveals reticulocytosis which is generally early and is hence most useful initial test of marrow erythroid hyperplasia. 2. Routine blood film shows macrocytosis, polychromasia and presence of normoblasts . 3. Bone marrow shows erythroid hyperplasia with usually raised iron stores. 4. X-ray o f bones shows evidence of expansion of marrow space, especially in tubular bones and skull.

11. III. Tests of damage to red cells Osmotic fragility is increased or decreased. Autohaemolysis test with or without addition of glucose. Coombs’ antiglobulin test. Electrophoresis for abnormal haemoglobins . Estimation of HbA2. Estimation of HbF . Tests for sickling . Screening test for G6PD deficiency and other enzymes (e.g. Heinz bodies test).

12. IV. Tests for shortened red cell lifespan. A shortened red cell survival is best tested by 51Cr labelling method. Normal RBC lifespan of 120 days . shortened to 20-40 days in moderate haemolysis and 5-20 days in severe haemolysis .

13. I. ACQUIRED (EXTRACORPUSCULAR) HAEMOLYTIC ANAEMIAS A. IMMUNOHAEMOLYTIC ANAEMIAS Immunohaemolytic anaemias are a group of anaemias occurring due to antibody production by the body against its own red cells. Immune haemolysis in these cases may be induced by one of the following three types of antibodies: 1. Autoimmune haemolytic anaemia (AIHA) characterised by formation of autoantibodies against patient’s own red cells. Depending upon the reactivity of autoantibody, AIHA is further divided into 2 types: i ) ‘ Warm ’ antibody AIHA in which the autoantibodies are reactive at body temperature (37°C). ii) ‘ Cold’ antibody AIHA in which the autoantibodies react better with patient’s own red cells at 4°C.

14. 2 . Drug-induced immunohaemolytic anaemia. 3. Isoimmune haemolytic anaemia in which the antibodies are acquired by blood transfusions, pregnancies and haemolytic disease of the newborn. An important diagnostic tool in all cases of immunohaemolytic anaemias is Coombs’ antiglobulin test for detection of incomplete Rh -antibodies in saline directly (direct Coombs’) or after addition of albumin (indirect Coombs’).

15. Conditions Predisposing to (AIHA) A. WARM ANTIBODY AIHA 1. Idiopathic (primary) 2. Lymphomas- leukaemias e.g. non-Hodgkin’s lymphoma, CLL, Hodgkin's disease. 3. Collagen vascular diseases e.g SLE 4. Drugs e.g. methyldopa, penicillin, quinidine group 5. Post-viral B. COLD ANTIBODY AIHA 1. Cold agglutinin disease a) Acute: Mycoplasma infection, infectious mononucleosis b) Chronic: Idiopathic, lymphomas 2. PCH ( Mycoplasma infection, viral flu, measles, mumps, syphilis)

16. ‘WARM’ ANTIBODY AIHA PATHOGENESIS . Warm antibodies reactive at body temperature and coating the red cells are generally IgG class antibodies and occasionally they are IgA . Human red cells coated with IgG antibodies are bound to the surface of RE cells, especially splenic macrophages. A part of the coated cell membrane is lost resulting in spherical transformation of the red cells (acquired spherocytosis ). Red cells coated with IgG along with C3 on the surface further promote this red cell- leucocyte interaction, accounting for more severe haemolysis . The spleen is particularly efficient in trapping red cells coated with IgG antibodies. It is, thus, the major site of red cell destruction in warm antibody AIHA.

17. CLINICAL FEATURES Warm antibody AIHA may occur at any age and in either sex. The disease may occur without any apparent cause (idiopathic) but about a quarter of patients develop this disorder as a complication of an underlying disease affecting the immune system such as SLE, chronic lymphocytic leukaemia , lymphomas and certain drugs such as methyl DOPA, penicillin The disease tends to have remissions and relapses. 1. Chronic anaemia of varying severity with remissions and relapses. 2. Splenomegaly . 3. Occasionally hyperbilirubinaemia

18. LABORATORY FINDINGS. 1. Mild to moderate chronic anaemia . 2 . Reticulocytosis . 3. Prominent spherocytosis in the peripheral blood film. 4. Positive direct Coombs ’ ( antiglobulin ) test for presence of warm antibodies on the red cell, best detected at 37°C. 5. A positive indirect Coombs ’ ( antiglobulin ) test at 37°C may indicate presence of large quantities of warm antibodies in the serum. 6. Unconjugated (indirect) hyperbilirubinaemia . 7. Co-existent immune thrombocytopenia along with occasional venous thrombosis may be present (termed Evans’ syndrome ). 8. In more severe cases, haemoglobinaemia and haemoglobinuria may be present.

19. ‘COLD’ ANTIBODY AIHA PATHOGENESIS . Antibodies which are reactive in the cold (4°C) may induce haemolysis under 2 conditions: 1. Cold agglutinin disease . In cold agglutinin disease, the antibodies are IgM type which bind to the red cells best at 4°C. These cold antibodies are usually directed against the I antigen on the red cell surface. Agglutination of red blood cells by IgM cold agglutinins is most profound at very low temperature but upon warming to 37°C or above, disagglutination occurs quickly. Haemolytic effect is mediated through fixation of C3 to the red blood cell surface and not by agglutination alone. Most cold agglutinins affect juvenile red blood cells.

20. 2. Paroxysmal cold haemoglobinuria (PCH). In PCH, cold antibody is an IgG antibody ( Donath -Landsteiner antibody) which is directed against P blood group antigen and brings about complement-mediated haemolysis . Attacks of PCH are precipitated by exposure to cold. PCH is uncommon and may be seen in association with tertiary syphilis or as a complication of certain infections such as Mycoplasma pneumonia, flu, measles and mumps.

21. CLINICAL FEATURES 1. Chronic anaemia which is worsened by exposure to cold. 2. Raynaud’s phenomenon. 3. Cyanosis affecting the cold exposed regions such as tips of nose, ears, fingers and toes. 4. Haemoglobinaemia and haemoglobinuria occur on exposure to cold. Treatment consists of keeping the patient warm and treating the underlying cause.

22. LABORATORY FINDINGS. 1. Chronic anaemia. 2. Low reticulocyte count since young red cells are affected more. 3. Spherocytosis is less marked. 4. Positive direct Coombs’ test for detection of C3 on the red cell surface but IgM responsible for C3 coating on red cells is not found. 5. The cold antibody titre is very high at 4°C and very low at 37°C ( Donath -Landsteiner test).

23. Isoimmune Haemolytic Anaemia Isoimmune haemolytic anaemias are caused by acquiring isoantibodies or alloantibodies by blood transfusions , pregnancies a nd in haemolytic disease of the newborn. These antibodies produced by one individual are directed against red blood cells of the other.

24. B. MICROANGIOPATHIC HAEMOLYTIC ANAEMIA Microangiopathic haemolytic anaemia is caused by abnormalities in the microvasculature. It is generally due to mechanical trauma to the red cells in circulation and is characterised by red cell fragmentation ( schistocytosis ). There are 3 different ways by which microangiopathic haemolytic anaemia results:

25. 1. EXTERNAL IMPACT . Direct external trauma to red blood cells when they pass through microcirculation, especially over the bony prominences, may cause haemolysis during various activities e.g. in prolonged marchers, joggers, karate players etc. These patients develop haemoglobinaemia , haemoglobinuria (march haemoglobinuria ), and sometimes myoglobinuria as a result of damage to muscles. 2. CARDIAC HAEMOLYSIS . A small proportion of patients who received prosthetic cardiac valves or artificial grafts develop haemolysis . This has been attributed to direct mechanical trauma to the red cells or shear stress from turbulent blood flow.

26. 3. FIBRIN DEPOSIT IN MICROVASCULATURE . Deposition of fibrin in the microvasculature exposes the red cells to physical obstruction and eventual fragmentation of red cells and trapping of the platelets. Fibrin deposits in the small vessels may occur in the following conditions: i ) Abnormalities of the vessel wall e.g. in hypertension, eclampsia , disseminated cancers, transplant rejection, haemangioma etc. ii) Thrombotic thrombocytopenic purpura . iii) Haemolytic-uraemic syndrome. iv) Disseminated intravascular coagulation (DIC) v) Vasculitis in collagen diseases.

27. D. PAROXYSMAL NOCTURNAL HAEMOGLOBINURIA (PNH) PNH is a rare acquired disorder of red cell membrane in which there is chronic intravascular haemolysis due to undue sensitivity of red blood cells to complement due to defective synthesis of a red cell membrane protein. The defect affects all the cells of myeloid progenitor lineage (RBCs, WBCs, platelets) suggesting a deficient haematopoiesis . The disorder generally presents in adult life.

28. PATHOGENESIS PNH is considered as an acquired clonal disease of the cell membrane while normal clone also continues to proliferate. The defect is a mutation in the stem cells affecting myeloid progenitor cells that is normally required for the biosynthesis of glycosyl phosphatidyl inositol (GPI) essential for anchoring of the cell; the mutant form of the gene is an X-linked gene called PIG-A ( phosphatidyl inositol glycan ). Thus, as a result of mutation, there is partial or complete deficiency of anchor protein. Out of about 20 such proteins described so far, the lack of two of the proteins— decay accelerating factor (DAF, CD55) and a membrane inhibitor of reactive lysis (MIRL, CD59), makes the RBCs unduly sensitive to the lytic effect of complement

29. CLINICAL AND LABORATORY FINDINGS ii) Pancytopenia (mild granulocytopenia and thrombocytopenia frequent). iii) Intermittent clinical haemoglobinuria ; acute haemolytic episodes occur at night identified by passage of brown urine in the morning. iv) Haemosiderinuria . v) Venous thrombosis as a common complication. The presence of inordinate sensitivity of red blood cells, leucocytes and platelets to complement in PNH can be demonstrated in vitro by Ham’s test using red cell lysis at acidic pH or by sucrose haemolysis test.