Direct identification of unexpected serum antibodies against red cell antigens

A new method to detect the identity of unexpected antibodies in the sera of prospective transfusion recipients is presented. The method is based on a macroscopic hemagglutination inhibition assay. In this assay, incubation of phenotypically defined test red blood cells with patient sera containing non-agglutinating antibodies to one or more specific antigen systems block monoclonal IgM induction of red cell agglutination. Since the specificities of the IgM antibodies are known, the identity of the patient's antibody(ies) can be directly determined. This method, which uses only reagents that are commercially available, is specific and eliminates the use of the indirect antiglobulin test (IAT) and the use of elimination panels.