What is the fundamental purpose of the crossmatch?

• A. Detect recipient antibodies directed against donor red blood cells
• B. Detect donor antibodies directed against recipient red blood cells
• C. Determine the blood type of donor
• D. Predict transfusion reactions with precision

Answer: (A)

Crossmatching serves to identify whether the recipient has antibodies that will react with the donor's red blood cells. By mixing the recipient’s serum with donor RBCs, we look for antibody binding that causes agglutination or hemolysis in the test system. If such antibodies are present, transfusing those donor cells could trigger a hemolytic transfusion reaction, so a positive crossmatch warns against using that donor blood. This is why the test is focused on detecting recipient antibodies against donor red cells.

It isn’t about detecting donor antibodies against the recipient, which isn’t the scenario tested. It isn’t about determining the donor’s blood type, which is done by ABO/Rh typing. And while a crossmatch reduces the risk of reactions, it doesn’t guarantee perfect prediction of all transfusion reactions, because reactions can arise from factors outside the crossmatched compatibility.