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Why must blood be tested and matched before a transfusion?

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Close-up illustration of multiple human red blood cells with their characteristic disc shape, floating against a red background. — blood group The major component of human blood is the red blood cell.

Blood must be tested and matched before a transfusion to ensure compatibility between the donor's red blood cells and the recipient's serum. This process is vital because the human immune system contains antibodies that will attack and destroy foreign red blood cells if they carry incompatible antigens.12

When incompatible blood is transfused, the interaction between donor antigens and recipient antibodies can cause hemolysis—the destruction of red blood cells—or dangerous blood clotting. Such reactions can lead to severe health complications, including fever or even death.231

Matching is primarily focused on the ABO blood group system and the Rh system. For example, if a person with type A blood receives type B blood, their anti-B antibodies will destroy the donor cells. Similarly, Rh-negative individuals who receive Rh-positive blood may develop anti-D antibodies, which can cause severe reactions in future transfusions or lead to erythroblastosis fetalis in subsequent pregnancies. Consequently, a direct match test is performed to confirm that the recipient's serum does not contain antibodies against the donor's cells.1243