Crossmatch before a blood transfusion

How is compatibility checked?

In a laboratory crossmatch, the recipient's plasma, the liquid part of blood, is tested against donor red blood cells. An electronic crossmatch instead uses validated computer checks. It is only suitable when the required blood-group and antibody checks meet specific criteria.

Blood grouping identifies markers such as A, B and RhD. An antibody screen looks for antibodies that might react with donor cells. Crossmatching brings these findings into the choice of a particular blood unit.

Why might another blood sample be needed?

Antibodies can appear after a previous transfusion or pregnancy. The laboratory therefore checks that the sample is still valid and reviews earlier results. Tell the team about any known red-cell antibodies, even if a recent screen was negative.