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Meaning and Uses of the Direct Antiglobulin Test

Meaning and Uses of the Direct Antiglobulin Test. Marilyn Telen, MD Duke University. Direct Antiglobulin Test. DAT Direct Coombs test Coombs test. Direct Antiglobulin Test. Test for in-vivo coating of patient’s red blood cells with anti-IgG and/or complement

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Meaning and Uses of the Direct Antiglobulin Test

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  1. Meaning and Uses of theDirect Antiglobulin Test Marilyn Telen, MD Duke University

  2. Direct Antiglobulin Test DAT Direct Coombs test Coombs test

  3. Direct Antiglobulin Test • Test for in-vivo coating of patient’s red blood cells with anti-IgG and/or complement • Washed patient’s red blood cells + polyspecific anti-human globulin (AHG: anti-IgG, anti-C3/C3d) • If positive, test red cells with 2 monospecific antibodies (anti-IgG and anti-C3) • If IgG+ may remove (elute) antibody and test for specificity

  4. Autologous Control • Positive autocontrol on panel can mean: • Alloantibody coating donor (previously transfused) red cells • Autoantibody

  5. Direct Antiglobulin Test • Physician request – usually because immune-mediated hemolysis is suspected. • Positive DAT could mean: • Warm autoantibody • Cold autoantibody • Transfusion reaction • Hemolytic disease of the newborn • Drug induced antibody • Drug adsorption - penicillin • Immune complex • Membrane modification • Induced autoimmunity

  6. DAT in Autoimmune Hemolytic Anemia (AIHA) • Warm AIHA – 80% of all AIHA • 99% have + DAT • 20% have IgG only • 67% have IgG + C3 • 13% have C3 only • Cold AIHA – 18% of AIHA • C3 only (antibody is IgM) • Paroxysmal Cold Hemoglobinuria – 2% of adult AIHA • C3 only or negative DAT

  7. Direct Antiglobulin Test • Transfusion Reaction work-up • DAT to detect antibody coating only donor cells in post sample • Immediate hemolysis • Prior work up missed detectable antibody • Delayed hemolysis • Antibody was below detectable levels on pretransfusion testing

  8. Direct Antiglobulin Test • Done with newborn type and screen • Hemolytic disease of the newborn • Maternal IgG antibody coating infant’s red cell • Anti-A, -B, -A,B • Alloantibody • Usually not due to Rh Immune Globulin

  9. Direct Antiglobulin Test A positive DAT does not necessarily mean hemolysis is really occurring. A large number of hospitalized patients (8-30%) have a positive DAT but no evidence of hemolysis. Frequency of + DAT increases with concentration of immunoglobulin, and thus presence of inflammation. About 1% of autoimmune hemolytic anemia will have a negative DAT.

  10. Direct Antiglobulin Test Useful in confirming immune-mediated hemolysis from a variety of causes. In combination with other tests, may help define cause of hemolysis. NOT indicative of hemolysis by itself.

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