Direct Coombs Test Or Direct Antiglobulin Test

The direct Coombs test (also known as the direct antiglobulin test) is used to detect antibodies on the RBC surface. A positive Coombs test indicates that an immune mechanism is attacking the patient's own RBC's. This mechanism could be autoimmunity, alloimmunity or a drug-induced immune-mediated mechanism.

The patient's RBCs are washed and then incubated with antihuman globulin. If immunoglobulin or complement factors have been fixed on to the RBC surface in-vivo, the antihuman globulin will agglutinate the RBCs and the direct Coombs test will be positive.

Examples of diseases that give a positive DAT: Rh isoiimunization, ABO disease, autoimmune hemolytic anemis (warm and cold type) and drug induced hemolysis.