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Test Findings

Direct Antiglobulin Test

March 3rd, 2020


The direct antiglobulin test (DAT), also known as the direct Coomb's, tests for IgG and complement 3 (C3) on the surface of red blood cells. The test is performed by adding antibodies against human IgG or C3 and monitoring for agglutination.
A positive test indicates an immune (autoimmune, alloimmune or drug-induced) cause of haemolysis, and may be positive before haemolysis occurs.
  • Causes of Positive Direct Antiglobulin Test

  • Normal in certain patients
  • False positive - clotted sample, poor testing technique, elevated serum immunoglobulins
  • Warm autoimmune haemolytic anaemia - idiopathic, lymphoproliferative disorders, infection, autoimmune disorders, methyldopa, penicillins, cephalosporins, rifampicin, quinine, paracetamol, ibuprofen
  • Cold agglutinin haemolysis - idiopathic, mycoplasma pneumoniae, EBV, lymphoma, paroxysmal cold haemoglobinuria
  • Alloimmune haemolysis - transfusion of mismatched red blood cells, haemolytic disease of the newborn, post stem cell transplant
  • Drug-induced haemolysis
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