Group A variants defined with a monoclonal anti-A reagent.

Unusual serologic findings mimicking the B(A) phenomenon were noted in two group B blood donors using blended murine monoclonal anti-A reagent. With additional studies, including a binding experiment using affinity chromatography, the presence of aberrant group A activities was confirmed. This observation suggests that persons with atypical B(A) phenotype may warrant further investigation to delineate the ABO blood group.