Which blood test must be performed prior to a blood transfusion?

The blood test that must be performed prior to a blood transfusion is the type and crossmatch. This test is crucial because it identifies the patient's blood type and ensures that the donor blood matches. The type determines the ABO and Rh (Rhesus) group of the patient's blood, which is vital in preventing transfusion reactions. The crossmatch involves mixing a small sample of the patient's blood with the donor blood to check for any incompatibility. If the blood types do not match, it can lead to serious and potentially life-threatening complications, such as hemolytic transfusion reactions. Therefore, performing a type and crossmatch is a fundamental step in safely administering a blood transfusion.

While a complete blood count provides useful information about blood cells, a blood culture detects infections, and a coagulation profile assesses clotting functions, none of these tests are specifically designed to ensure compatibility between the donor and recipient blood. Thus, the type and crossmatch is the key test to perform prior to a transfusion.