Unexpected occurrence of anti-B antibodies in a patient with A2B blood group: a case report and review of literature.

Background: The ABO blood group system categorizes human blood according to the inherited characteristics of erythrocytes, which are defined by the presence or absence of antigens A and B located on the surface of red blood cells. In the absence of these antigens, the body produces natural antibodies.

Case presentation: In this case report, we present a 42-year-old man of Iranian (Persian) ethnicity who was a blood donor at the Arak transfusion center. Forward and reverse typing showed a discrepancy, with AB as the cell type and O blood group as the back type results.

Conclusion: This report shares our experience of unexpected anti-A and anti-B antibodies presence in AB blood group. Finally, it was discovered that the patient has an A2B blood group with clinically insignificant anti-A1 antibodies. The reason behind the occurrence of B antibodies in this case is still unknown but can be considered an acquired B phenomenon. To the best of our knowledge, this is the first report of anti-B antibodies in a patient with an A2B blood type in Iran.