• The final test confirming compatibility performed on blood about to be transfused is called the crossmatch. In this test, a sample of RBCs from the specific unit of blood selected for transfusion is tested against the patient’s plasma.
• After grouping and antibody screening have been performed, the main purpose of crossmatching is to confirm ABO compatibility between the donor and the recipient of a blood transfusion.

There are three main types of crossmatching tests:

• Immediate spin crossmatch – this test which takes 5-10 minutes is performed at room temperature and confirms ABO compatibility as the patient’s plasma is tested against donor RBCs and observed for agglutination and/or hemolysis.
• Antiglobulin crossmatch – this test which takes 30-60 minutes is performed at 37°C and an antiglobulin test is carried out on the mixture of patient’s plasma and donor RBCs to check for agglutination. This test is mandatory for patients with RBC alloantibodies.
• In the electronic crossmatch, a computer matches compatible units of blood from the blood bank to patients directly.