How does crossmatching donor blood with recipient blood work?

Crossmatching, or the direct match test, is a vital safety procedure in blood transfusion used to ensure that donor blood is compatible with the recipient’s immune system.1

The process works by testing the recipient’s serum against the donor’s red blood cells to detect the presence of antibodies that might react with the donor's antigens. This is typically performed using the direct match test and the indirect Coombs test, which screen for both naturally occurring and immune antibodies.1

If these tests indicate that the recipient’s serum contains antibodies capable of attacking the donor’s cells, the blood is deemed incompatible and must not be used, as such a reaction could lead to a hemolytic transfusion reaction and potentially death. This rigorous testing is essential because even if blood types are ABO and Rh compatible, other minor antigens or antibodies to platelets and white cells can still trigger adverse reactions.12