Coombs’ Test, Indirect
Test Description The indirect Coombs’ test is used to detect unexpected circulating antibodies in the patient’s serum which may react against transfused red blood cells. These antibodies are ones other than those of the A, B, and O blood groups. This is different from the direct Coombs’ test, which detects antibodies already attached to the red blood cells. In this test, the patient’s serum is considered the antibody and the donor red blood cells as the antigen. The serum and antigenic red blood cells are brought together to allow any antibodies to attach to the red blood cells. Antihuman globulin is then added. If the patient’s serum contains an antibody that reacted with and attached to the donor red blood cells, agglutination will occur and the test is considered positive. If no agglutination occurs, no antigen-antibody reaction has taken place. The serum may contain an antibody, but the donor red blood cells do not have the antigen against which the antibody would ...