A1 and A2 Sub-Types of Blood Group 'A': A Reflection of their Prevalence in North Karnataka Region.

INTRODUCTION: Landsteiner ABO system of blood groups is most important for transfusion medicine and has subtypes of A Antigen, A1 and A2, upon which further groups of A and AB have been classified. Of individuals with A antigen, approximately 20% belong to A2 while rest 80% belong to A1. Anti-A1 Lectin, a cold agglutinin which destroys A1 cells is clinically significant when they react at 37°C, causing transfusion reactions.

AIM: To assess the prevalence of A1 and A2 subgroups in the population.

MATERIALS AND METHODS: This was two year retrospective analysis of blood groups of donors coming to the blood bank of Karnataka Institute of Medical Science, Hubli, Karnataka, India. The data of the subgroups A and AB was analysed.

RESULTS: 20,864 donors were analysed. Of 5466 (26.20%) of A group, 5406 (98.90%) belonged to A1 subgroup and only 60 (1.10%) belonged to A2 subgroup. Of 1708 donors with blood group AB, 1532 (89.70%) belonged to A1B subgroup and 176 (10.30%) belonged to A2B. It was noted that A2 in AB blood-group, as A2B, was more frequent in occurrence than presence of A2 as an A blood group. Rhesus negative frequency in these subgroups was also reported.

CONCLUSION: Having known the prevalence of A1 and A2 subgroups and incorporating them into the ABO grouping system can limit these minor, yet dangerous, transfusion incompatibilities.