Diminished expression of B antigen mimicking B3 phenotype in a patient with AML-M3: a rare case report

The ABO blood group system plays an important role in transfusion and transplantation practices. Correct identification of the blood group of an individual is of paramount importance as minor errors can lead to fatal transfusion reactions. Weak expression of A, B and H antigens on the red cell surface can be inherited or acquired. They are probably the least frequently encountered and pose a challenge in the routine immunohematology practice.1 Such antigenic changes in hematological malignancies most commonly involve the ABO blood group system.2 The strength of agglutination with anti-B, anti-A,B, and anti-H serum, presence or absence of ABO isoagglutinins in the serum, adsorption-elution studies and the presence or absence of A, B and H substance in saliva along with pedigree analysis help to characterize the weaker variants of A and B serologically. Possible phenotypic subgroups include A3, Aend, Ax, Am, Ay, and Ael. Subgroups of B are very rare, less frequent than those of A and are classified as B3, BX, Bm and Bel in decreasing order of the amount of the B antigen (Table 1).