Significant ABO hemolytic disease of the newborn in a group B infant with a group A₂ mother

ABO hemolytic disease of the newborn (HDN) occurs almost exclusively in infants of blood group A or B who are born to group O mothers because IgG anti-A or -B occurs more commonly in group O than in group A or B individuals. We report a case in which clinically significant ABO-HDN occurred in a group B neonate from anti-B of a group A₂ mother. The IgG anti-B titer was much higher (256) than that found in a group A₁ mother/infant control group (≤ 32). The maternal antibody screen was negative and antibodies to low-frequency antigens were not detected. Therefore, when evaluating unexplained HDN in a group B newborn of a group A mother, it may be relevant to determine the subgroup of the mother. As presented here, anti-B from a group A₂ mother may, on occasion, be responsible for HDN. Immunohematology 2000;16: 105–108.