How many different types of crossmatches are there and how does the laboratory decide which should be performed?
There are basically three types of crossmatch (compati-bility) tests: the computer crossmatch, the immediate spin crossmatch, and the antiglobulin crossmatch. The antiglobu-lin crossmatch may use any one of several different enhanc-ing media and may be performed in solution, on a solid phase support, or in a gel medium.
Standards require that every sample used for compati-bility testing be tested for ABO group, Rh type, and unex-pected antibodies to red cell antigens. A specific type of test is not recommended, but standards require that the test methods demonstrate clinically significant antibodies, and include incubation at 37°C preceding an antiglobulin test using unpooled reagent red cells. If red cell antibodies are detected, the method used for crossmatching must demon-strate ABO incompatibility, must detect clinically signifi-cant antibodies, and must include an antiglobulin test. If no clinically significant antibodies are detected, and there is no prior history of immunization to red cell antigens or of transfusion reactions, then at a minimum, the cross-match technique must demonstrate ABO compatibility. The immediate spin crossmatch involves mixing donor red cells with patient serum followed by centrifugation, and examination of the suspension for red cell agglutination. This technique detects ABO incompatibility but does not detect incompatibility for other clinically significant blood groups. However, a computer system instead of the imme-diate spin crossmatch may be used to detect ABO incom-patibility provided the following conditions have been met:
· The computer system must have been validated on-site to ensure that only ABO-compatible red cell products have been selected for transfusion.
· Two determinations of the recipient’s ABO group are made, either by testing the same sample twice or by test-ing of two current samples.
· The system contains complete blood group information and unique identifiers for the product and the recipient.
· A method exists to verify correct entry of data.
· The system contains logic to alert users to discrepancies in the donor product testing record, and ABO incompat-ibility between donor and recipient. If no clinically significant antibodies are detected, but there is a past history of immunization to red cell antigens, or a history of transfusion reactions, an antiglobulin crossmatch must be performed.