Identification of a Subset of Group B Donors Reactive with Monoclonal Anti-A Reagent

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Abstract
Two red blood cell (RBC) units labeled group B were returned to the source blood center after they had been retyped as AB by a transfusion service. The discrepancy could be reproduced, but only with the use of the transfusion service’s reagent, Ortho Diagnostic’s anti-A Bioclone® (a licensed, blended, murine monoclonal anti-A reagent). RBCs from 35 of 3,458 random group B donors (1%) reacted with the monoclonal anti-A after immediate centrifugation. Reactivity was associated with high serum levels of B-gene-specified transferase and was caused by the MH104 component, a potent anti-A capable of detecting some examples of Ax RBCs. It is probable that the potency of MH04 permitted detection of low levels of A determinants synthesized by the donors’ unusually strong B-gene-specified transferase. Transfer of N-acetylgalactosamine by B-gene-specified transferases, reported in vitro, has not been detected previously in vivo. Use of highly sensitive monoclonal reagents may result in clinically ambiguous blood grouping results.