Type and Screen/Match

When blood is ordered the patient’s blood is typed and the patient’s serum is tested for unexpected antibodies to red cell antigens (antibody screen) and for reactivity against antigens present on donor red cells (compatibility test or crossmatch test). The compatibility test is valid for 3 days after the blood sample is drawn. Validity of compatibility testing is limited to 3 days because the patient’s antibody status may change. If the physician determines that transfusion is necessary after 3 days, a fresh sample must be drawn.

Although compatibility testing does not guarantee a patient will not have a reaction, it is the best protection against acute hemolytic transfusion reactions. Crossmatched blood should always be requested unless emergent clinical situations dictate otherwise.