An essential goal in transfusion medicine is that transfused blood be compatible with the patient. The clinical and serologic evaluation, which allows for the transfusion of the most compatible (or "least incompatible") blood, requires a joint effort between the clinician and the transfusion medicine physician .
However, there are times when all available resources are exhausted and a unit of blood that is not crossmatch compatible must be issued to the patient. The most common of these clinical situations as well as suggestions on how safely to issue and transfuse the best unit of blood available will be reviewed here. General discussions of crossmatching procedures and red cell antigens are presented separately. (See "Red blood cell compatibility testing (crossmatching)" and "A primer of red blood cell antigens and antibodies".)
When blood is ordered for transfusion, a sample of blood is obtained from the patient, and the transfusion service typically performs type and screen and crossmatching tests on the patient's red blood cells (RBCs) and plasma:
●A type test of the patient's RBCs to determine the ABO and Rh types. (See "Red blood cell compatibility testing (crossmatching)", section on 'Specimen requirements'.)
●An antibody screen of the patient's plasma to determine if unexpected anti-RBC antibodies are present. (See "Red blood cell compatibility testing (crossmatching)", section on 'Antibody detection'.)