The utility of an acid elution when a direct antiglobulin test is positive due to complement alone

Acid elutions are intended to recover IgG antibodies from the red blood cell (RBC) surface. Eluates from samples that are direct antiglobulin test (DAT) positive with complement (C3) only would be expected to be negative. However, elution studies performed on RBCs that are DAT positive with C3 only can produce clinically significant results. Identifying how often clinically relevant information is obtained when elutions are performed on samples DAT positive with C3 alone would aid in developing guidelines for elution performance on these samples and reducing performance of eluates on such samples with clinically insignificant results. Patient samples that are DAT positive with C3 only submitted over an 11.5-month period at the American Red Cross' Immunohematology Reference Laboratory locations were identified. The eluate result, serum result, transfusion history, and patient diagnosis were captured and analyzed. In total, 1171 samples that were DAT positive with C3 only were identified and, of those, 321 (27%) samples had an elution performed. A nonreactive eluate was the most common result. Alloantibodies were identified in 19 (6%) eluates. Panagglutination/autoantibodies was identified in 71 (22%) eluates. Informative eluates were identified as those eluates showing any alloantibody, regardless of serum results, or panagglutination/autoantibody present in the eluate but not concurrently present in the serum (n = 30,9%). Guidelines based on recent transfusion history, indicators of active hemolysis, and autoimmune reactivity concurrently in the serum should be implemented to identify clinically significant information and to reduce the number of uninformative elutions performed.