Rare subgroup of A phenotype—a case series

Testing for ABO incompatibility between a potential blood donor and recipient is the cornerstone of pretransfusion testing. Occasionally, weak agglutination reactions occur due to low expression of A and B antigens on the surface of red blood cells. This can lead to inconsistencies in blood group typing, as seen in a case where a patient’s forward and reverse typing showed discrepancies. Following a comprehensive analytical assessment, the patient was identified as having a distinctive variant of blood group A, belonging to the less common subgroups—A₃, A_end, A_x, A_m, A_y, and A_el. Herein, we present 3 case series of ABO subgroups identified through extended ABO blood grouping procedures.