ABO grouping is based on the presence of antigens on the Red Blood Cells (RBCs) and antibodies in the plasma. Individuals with blood group AB possess both Antigen A and Antigen B on their RBCs, but their plasma contains no antibodies (neither anti-A nor anti-B). The absence of antibodies allows them to accept blood from any donor group (A, B, AB, or O) without an immune reaction, making them 'universal recipients' , .