Purpose of Cross Matching
The crossmatch is routinely used as the final step of pretransfusion compatibility testing. The purposes of compatibility testing are to detect: irregular antibodies; errors in ABO grouping, and clerical errors in patient identification and result recording. The crossmatch will detect the following:
1. Most recipient antibodies directed against antigens on the donor red blood cells.
2. Major errors in ABO grouping, labeling, and identification of donors and recipients.
Cross-matching will detect incompatibilities between the donor and recipient that will not be evident on blood typing. There are two types of cross-matches: Major cross-match and Minor cross-match.
The major crossmatch involves testing the patient’s serum with donor cells to determine whether the patient has an antibody which may cause a hemolytic transfusion reaction or decreased cell survival of donor cells. This is the most important cross-match.
The minor crossmatch involves testing the patients cells with donor plasma to determine whether there is an antibody in the donor’s plasma directed against an antigen on the patient’s cells.
- Prepare donor and recipient blood samples:
For Major crossmatch : Donor’s red cell and recipient serum or plasma
For Minor crossmatch : Recipient red cells and donor’s serum or plasma
- Prepare 3 – 5% cell suspensions of red cells.
- Major Crossmatch:
Label a test tube. Add two drops of the patient serum and one drop of the appropriate donor cell suspension.
- Minor Crossmatch:
Label a test tube. Add two drops of the appropriate donor serum and one drop of the patient cell suspension.
- Mix the tubes and incubate at 37°C for about 45 minutes.
- Add two drops of AHG (Antihuman globulin) and mix well.
- Centrifuge for 1 minute at 1500 rpm
- Read macroscopically and microscopically and record the results
The mixture of erythrocytes and serum are observed for hemolysis or microscopically for agglutination. Any evidence of hemolysis/agglutination indicates an incompatible cross-match. Negative results are taken to indicate compatibility.