Detection of a weaker subgroup of A in ABO blood group system

Testing to detect ABO incompatibility between a donor and potential transfusion recipient is the foundation on which all other pretransfusion testing is based. Sometimes, weak agglutination reactions may be obtained with reagent antibodies due to weak expression of A and B antigens on red blood cell (RBC) surface which may cause a discrepancy in blood group typing. Here, we report a patient showing discrepancy between RBCs (forward) and serum (reverse) typing. After doing detailed analysis, the blood type as a variant of blood Group A revealed. Subgroups of A are very rare phenotype of blood. Weaker subgroups of A blood group reported so far are mainly A₃, A_end, A_x, A_m, A_y, and A_el. We are reporting a case of a 35-year-old patient whose RBCs showed a discrepancy between cell and serum grouping during initial testing. Serological investigation included absorption elution tests and saliva tests after performing initial blood grouping. The serological characteristics of the patient's red cells were similar to A₃ subtype. The patient was a secretor and A and H substance was present in the saliva. Serum did not show any presence of anti-A1. The weak A phenotype identified had serological characteristics similar to A₃.