Discrepancy in ABO Blood Grouping: A Report of B Subgroup with Cold Alloantibody

The ABO antigens are the most important in both blood transfusion and transplantation as their antibody can cause severe haemolytic transfusion reaction when ABO-incompatible transfusion occurs. It has been claimed that variants of the ABO blood group are very rare, including B subgroups. We reported a young healthy female with B subgroup and underlying cold-reacting alloantibody causing challenges in determining of her ABO blood group. Initial ABO blood grouping was misinterpreted as group O. Presence of alloantibody in her plasma was suspected after revealing positive antibody screening. Repeated blood grouping at 37oC revealed a discrepancy of the forward and reverse grouping, which suggested B subgroup. Cross-matching showed difficulties in finding compatible blood with both group O and B cells due to the presence of clinically significant cold alloantibody. Determining of correct ABO blood group is mandatory in transfusion practices as haemolytic transfusion reaction can be prevented.