Warm reactive anti-A₁ agglutinin in an A₂B individual: A rare case with review of literature

The prevalence of the major subgroup of A as A₁ in almost 80% of the A group population is a known fact. A₂ and the remaining subgroups such as A_end, A_m, A_x etc comprise the remaining population, based on erythrocyte agglutinability and various serological reactions. These A subgroups can often result in an ABO typing discrepancy. Anti-A₁ antibody often appears as an irregular cold agglutinin in the sera of A₂ or A₂B individuals who lack the corresponding antigen. Rather notably, the literature suggests that 1% to 8% of A₂ and 22% to 35% of A₂B individuals possess an allo-anti-A₁ in their sera, which reacts at a temperature below 25°C. Although routinely, it does not pose any problem either during or post blood transfusion, however, the literature reports of hemolysis happening in procedures that are performed at lower temperatures, particularly in hypothermic situations. We report herein, a case of a massively bleeding A₂B Indian lady after the expulsion of her dead fetus and an underlying uterine fibroid having a warm reactive allo-anti-A₁ agglutinin that warranted an urgent blood transfusion management.