ABO discrepancy with monoclonal ABO reagents caused by a pH-dependent autoantibody

ABO discrepancy was noted when a patient’s unwashed saline red cell suspension was tested with monoclonal ABO reagents. The discrepancy was resolved when a washed (× 3) saline red cell suspension was used in repeat testing. The patient’s serum contained an autoagglutinin that reacted optimally below pH 7.0. Tire discrepancy occurred when monoclonal ABO reagents, formulated at a low pH, lowered the pH of the reaction mixture, and autoagglutination was observed. Immunohematology 1995;11:71–73.