ABOmismatch

ABOmismatch refers to incompatibility between donor and recipient blood types based on the ABO blood group system. It arises because ABO antigens are expressed on red blood cells and other tissues, while naturally occurring anti-A and anti-B antibodies in plasma can react against non-self antigens. ABO mismatch is clinically relevant in blood transfusion, solid-organ transplantation and hematopoietic stem cell transplantation.

Three categories are commonly described: major mismatch (recipient has antibodies against donor red cells), minor mismatch (donor plasma contains antibodies against recipient red cells) and bidirectional mismatch (both parties have antibodies against the other). In transfusion, a major mismatch can cause an acute hemolytic transfusion reaction with intravascular hemolysis, hemoglobinuria, renal injury and shock. In solid-organ transplantation, ABO incompatibility historically produced hyperacute antibody-mediated rejection, but modern desensitization and immunosuppressive protocols have reduced this risk in selected settings. In hematopoietic stem cell transplantation, ABO incompatibility does not preclude transplantation but can cause hemolytic complications and delayed erythroid recovery.

Prevention centers on careful blood typing, compatibility testing and crossmatching. Management when incompatibility is unavoidable includes use of compatible or modified blood products (plasma reduction, washed red cells), antibody removal techniques (plasmapheresis, immunoadsorption), and targeted immunosuppression such as rituximab. Clinical outcomes depend on the context, antibody titre, and promptness of recognition and treatment.