Serologic test used in all transfusion services and reference labs; also known as the “Indirect Coombs” test or the simple abbreviation, “IAT.” This test is done to detect antibody and/or complement coating red cells following incubation with serum or plasma in the laboratory (the Direct Antiglobulin Test detects the same thing, but the interaction between antibody/complement and red cells occurs in the body). The IAT is used in routine pretransfusion testing to detect patient red cell antibodies as the essential part of every antibody screening test or antibody identification panel, and it is also used in major crossmatches to detect possible incompatibility when the patient has a current or historical clinically significant red cell antibody.