Studies of antibodies in the sera of patients who have made red cell autoantibodies.

Background: In patients in whom autoantibodies of broad specificity (panagglutinins) are present in the serum, adsorption studies are often necessary to identify alloantibodies that are simultaneously present.

Study Design And Methods: Samples from 138 patients in whom the direct antiglobulin test was positive and antibody was present in the serum were studied. When antibody identification studies before or after initial adsorption suggested the presence of an alloantibody, additional alloadsorptions were performed.

Results: Among the samples from 138 patients, 71 contained only panagglutinating autoantibody, and another 19 contained either autoantibodies or alloantibodies that were not accompanied by panagglutinins. The remaining 48 samples contained both panagglutinins and a total of 62 antibodies that appeared to be alloimmune in nature. Alloadsorption with antigen-negative red cells showed that 29 (47%) of the apparent alloantibodies were in fact partially adsorbed autoantibodies that mimicked alloantibodies by their reactions.

Conclusion: Initial autoadsorption often left unadsorbed alloantibodies and autoantibodies with mimicking specificities. Initial alloadsorption more often left only true alloantibodies unadsorbed. From the screening tests, it appeared that 43 percent of the 138 patients were alloimmunized. Recognition of the mimicking nature of the partially adsorbed autoantibodies found that the real incidence of alloimmunization in the patients was 23 percent. Recognition of this phenomenon considerably simplifies the selection of blood for transfusion to these patients.