The direct antiglobulin test (DAT; direct Coombs test) is performed by adding anti-human globulin to patient RBCs. The indirect antiglobulin test (IAT; indirect Coombs test) is performed by adding patient plasma to test RBCs followed by the addition of anti-human globulin. In either case, the presence of an anti-RBC antibody (autoantibody or alloantibody) causes RBCs to be agglutinated when the anti-human globulin is added.
- DAT: Agglutination occurs when anti-human globulin (green) crosslinks an anti-RBC antibody (blue) that is bound to an antigen on patient RBCs.
- IAT: Agglutination occurs when anti-human globulin (green) crosslinks an anti-RBC antibody (blue) in patient plasma or serum to which test RBCs are added.
Refer to UpToDate topics on pretransfusion testing and immune hemolytic anemia regarding uses of these tests.
