Cross Match Test

Cross Match Test

Importance

The final decision of whether donor blood is safe to transfuse to a patient does not depend solely on the grouping and Rho (D) typing; but it depends on whether the two bloods are compatible i.e. whether there is any hemolysis or agglutination when they are mixed together. Under most circumstances, if grouping and typing tests have, been performed accurately and if donor blood of the same group and type has been selected for transfusion, they will be found to be compatible. However, there are occasions when,

(1) The donor may have antibodies in his serum or

(2) The patient may have antibodies in his. serum or

(3) There may have been a mistake in performing, reading or recording of the blood grouping and Rho (D) typing results. Considering all these possibilities, a compatibility test is essential before all transfusions. Test for compatibility is performed in the blood bank laboratory. If there is any Incompatibility, the transfusion of incompatible blood can be prevented. The procedure used to determine compatibility of donor and recipient’s blood is called the cross match. This procedure is performed in two parts,

(1) Major Cross Match i.e. the donor’s cells are mixed with the patient’s serum

(2) Minor cross match: The patient’s cells are mixed with the donor’s serum.

Requirements

1. Small test tubes
2. Pasteur Pipettes
3. Normal Saline
4. Centrifuge

Specimen

1. Patient’s blood and serum
2. Donor’s blood and serum

Procedure

1. Prepare 5% cell suspensions of patient’s blood (P) and donor’s blood (D) in two separate tubes.
2. To the patient’s tube (P), add two drops of patient’s serum and one drop of donor cell suspension (major side).
3. To the Donor’s tube (D), add two drops of donor’s serum and one drop of patient’s cell suspension (minor side).
4. Mix the contents of both the tubes gently and keep the tubes at room temperature for 30 minutes. Centrifuge at 1,500 RPM for one minute.
5. Examine for the agglutinations both macroscopically and also microscopically.

Direct Coombs Test ?

What is Indirect Coombs Test ?

Interpretation

1. Blood which shows a major incompatibility should never be transfused.
2. The minor cross-match results are also important. But in an emergency it is possible to use blood which is minor incompatible, (but not major compatible) without leading to a transfusion reaction. This is because of the fact that, in the patient’s body the ‘minor side’ would be the donor plasma (about 200 to 300 ml). This may contain the antibodies. But these antibodies will get mixed and diluted with about 2,500 ml of patient’s serum so that there will not be a major reaction. Only following two conditions may show significant incompatibility:
   • a) High titer of donor antibodies and
   • b) Multiple transfusions. of minor incompatible blood.

Additional information

1. The saline tube method requires longer incubation but weak reactions are detected better by this method.
2. For faster results, after mixing the cells and serum, keep the tubes at room temperature (25°C ± 5°C) for 5 minutes and then centrifuge at 1,500 RPM for one minute. Resuspend the cells and observe for agglutinations. If the resuspended cells are without any clumps, then proceed to the next step-
   • a) Add two drops of 22% bovine albumin and incubate the tubes at 37°C for 15 minutes. Centrifuge at 1500 RPM for one minute.
   • b) Examine macroscopically and microscopically for agglutinations.

Note :-

1. Centrifugation brings the cells into close proximity and hastens the agglutination.
2. Incubation at 37°C may detect some ‘warm’ antibodies missed in room temperature incubation.
3. The Bovine albumin reagent (22%) added may detect some incompatibilities, (not detected in saline) due to incomplete immune antibodies such as Rh antibodies.