A laboratory test for the presence of complement or an antibody that is bound to a patient’s red blood cells. The test is used in patients with autoimmune hemolytic anma, hemolytic disease of the newborn, and transfusion reactions. After the patient’s RBCs are washed to remove unbound antibodies, they are mixed with antihuman globulin serum containing polyvalent antibodies that bind with the antibody or complement on the RBCs and cause them to agglutinate (clump). Monoclonal antibodies can be used to identify the specific class of antibody or complement component causing RBC destruction.