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

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.

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

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.

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.

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.