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, Aend, Ax, Am, Ay, and Ael. Herein, we present 3 case series of ABO subgroups identified through extended ABO blood grouping procedures.