Blood Compatibility Testing

A "type" includes a "front type" and a "back type". The "front type" determines which antigens ("flags") in the ABO blood group system are on the patient's red blood cells as follows:

A antigen only ------------Type A

B antigen only -------------Type B

A and B antigens -----------Type AB

Neither A or B------------ Type O

anti-B ------------- Type A

anti-A ------------- Type B

anti-A and anti-B ------------ Type O

neither anti-A or anti-B -------------Type AB

In addition, RBC's are Rh typed and identified as "D" positive or negative.

A "screen" looks for unexpected red cell alloantibodies which may form following pregnancy or prior transfusions. If the screen is positive, the antibody is identified and 2 units lacking the corresponding antigen are crossmatched for the patient. The physician is also notified. Antibody identification can be complicated and take more than a day to complete.

A "type and cross" determines compatibility between patient serum and donor red blood cells.

A full crossmatch procedure takes about 45 minutes to complete and cannot be shortened.

Units are refrigerated until used.

A unit of blood must be properly labelled and the label MUST be checked before use.

Every unit crossmatched is removed from the general inventory and reserved for the patient for 72 hours. Units which are crossmatched unnecessarily will deplete Blood Bank inventories and can result in blood shortages, such as those which occurred in California after the earthquake. Blood shortages can result in cancellation of elective surgical procedures.

Blood will ordinarily not be released for transfusion until compatibility testing is completed.

However, under emergency conditions, blood products may be released without a crossmatch if the patient is in danger of dying if transfusion is delayed. In such cases, if the patient's blood type is not known, then group O Rh negative (O neg) blood can be released without compatibility testing.

In cases in which the patient's blood type is reliably known, then type-specific blood or RBC's of the same ABO and Rh group may be released.