Haemolytic Anaemias due to Extrinsic Factors
Immune Haemolytic anaemias (IHA)Definition and Classification
Immune haemolysis is defined as red cell destruction brought about by antibody antigen reaction, antibodies are usually directed against red cell antigens. The defining character of all IHA is a positive direct antiglbulin ( DAT or Coomb’s ) test. Classification:Autoimmune H. A.: Antibodies produced by the individual himself Warm antibody typeCold antibody type ( cold agglutinin syndromes)Alloimmune H.A : antibodies and antigens belong to different individuals:Haemolytic disease of the newborn ( HDN).Incompatible blood transfusion.Drug induced IHA:Warm AB type AIHA
The antibody is IgG and has a maximal activity around 370C. Antibody coated RBCs are destroyed extravascularly by the cells of the RE system mainly in the spleen. The disease affects females more commonly, the onset is usually insidious with jaundice , anaemia and splenomegaly. Haematologically: RBCs are normochromic, normocytic with spheroctosis, normoblastaemia and marked reticulocytosis.Aetiology of warm type AIHA
Idiopathic in 30 % of cases. Secondary to: Lymphoproliferative disorders ( CLL, HD and NHL ) Autoimmune disorders ( SLE, RA and ulcerative colitis ). Infections ( viral ) Carcinomas ( ovarian ca. ) Drugs ( methyldopa )
Diagnosis of warm type IHA
Diagnosis depends on:Clinical findingsClassical red cell morphology.A positive direct Coomb’s testIf transfusion is needed, these patients present a problem to the blood bank as it is almost impossible to find a compatible blood, usually the least incompatible unit is chosen from a panel of blood units.Haemolytic Disease of the Newborn ( HDN )
Destruction of fetal RBCs by maternal AB. Maternal IgG AB can pass the placental barrier and react with fetal red cell antigens, more commonly with antigens in the ABO and Rh systems. ABO HDN occur in blood group O+ mothers who have in their sera immune anti-A & anti-B antibodies and carry a blood group A , B or AB fetus, the disease is most commonly mild and presents as NNJ, rarely needs exchange transfusion, it can affect the first pregnancy.Rh HDN ( Erythroblastosis fetalis )
This is more serious than ABO HDN, first born baby is not affected, but at the time of delivery fetal RBCs pass to maternal circulation and the mother may become sensitized ( produces anti-D antibodies ), the second baby will usually have severe anaemia with severe jaundice ( 2nd or 3rd day ) and may develop kernicterus with severe neurological defects unless promptl;y treated by exchange transfusion, subsequent deliveries result in still birth, the fetus has gross pallor, oedema , jaundice and gross abdominal distension with a bulky placenta ( hydrops fetalis ). Rh HDN affects only about 30% of Rh-ve mothers carrying Rh+ve babies, ABO fetomaternal incompatibility reduces sensitization. The blood picture shows anaemia with reticulocytosis and normoblastaemia ( erythroblastosis fetalis ).Mechanical anaemias Fragmentation Anaemias
Fragmentation anaemias are group of haemolytic anaemias characterized by presence of fragmented RBCs in the peripheral blood ( Schistocytes )and intravascular haemolysis.Fragmentation anaemias could result from:Prosthetic cardiac replacements ( valves and patches ), associated with turbulent blood flow ( cardiac haemolysis )Red cell destruction in the small blood vessels “ micro-angiopathic haemolytic anaemia ( MAHA ) “ as a result of :Wide spread fibrin deposition ( DIC )Abnormal platelet aggregation ( platelet aggregate syndromes ; HUS & TTP ).Abnormal vascular endothelium ( vasculitis ) MAHA is characterized by thrombocytopenia in addition to schistocytosis & features of intravascular haemolysis.