Clinical approach after identification of a rare anti-En^a in a prenatal sample

The antigens associated with the MNS blood group system (ISBT 002) are located on glycophorin A (GPA) and glycophorin B (GPB). The most frequently encountered antibodies to antigens in this system by a transfusion medicine service are those directed against M, N, S, and s. Individuals lacking GPA typically have red blood cells that lack M, N, and En^a, whereas those lacking both GPA and GPB lack M, N, and En^a as well as S, s, and U. Such individuals may develop a rare antibody, anti-En^a, directed against determinants on GPA. This antibody is capable of causing hemolytic transfusion reactions and hemolytic disease of the fetus and newborn. This case report describes a pregnant woman found to have anti-En^a. Molecular testing supported an M^k phenotype that was found in several members of her immediate family.