CROSS MATCHING (Major cross match, Minor cross match:

CROSS MATCHING (Major cross match, Minor cross match:-)

CROSS MATCHING:- Before a donor's blood is transfused into a recipient, there should be no antigens or antibodies in both the donor's blood and recipient's blood that would react with each other, resulting in the destruction of red cells. In other words, there should be no transfusion reaction. The donor's blood should be compatible with recipient's blood and should give maximum benefit to the recipient.

 Crossmatching is divided into two parts:

1. Major cross match:- It involves testing donor's red cells with recipient's serum to detect unexpected antibodies in recipient's serum that will destroy donor's red cells.

2. Minor cross match:- It tests recipient's red cells with donor's serum in the same way as the major cross match. These antibodies can also be detected by antibody screening tests.

Method of crossmatching

Methods  1: saline method

A.   Slide method

1.     Prepare 5% washed red cells suspemsions of the doner and recipient red cells in saline properly labeled tubes.

2.     Divide the slide in two parts, major and minor, as shown below.

Major cross match	Donor cells + Recipient serum
Minor cross match	Recipient cell + Donor serum

3. To the 'major part of the slide, add one drop of recipient's serum and one drop of donor's red cell suspension. Mix with an applicator stick.

4. To the 'minor' part of the slide, add one drop of donor's serum and one drop of recipient's red cells. Mix.

5. Allow to stand at room temperature for 5-10 minutes in a moist chamber.

6. Examine both macroscopically and microscopically for agglutination.

Note:- The results should be read as soon as possible because drying of the suspension may show false agglutination.

Interpretation Compatible donor and recipient blood should show no agglutination in both the major and the minor crossmatch.

B.   Tube method

1. Prepare 5% washed red cell suspensions of donor's and recipient's red cells in appropriately labelled tubes.

2. In a test tube labelled 'major', mix one drop of donor's red cells and two drops of recipient's serum.

3. In another tube labelled 'minor', mix one drop of recipient's cells and two drops of donor's serum.

4. Allow the tubes to stand at room temperature for five minutes. Centrifuge at 1000 g for 15-20 seconds.

5. Examine macroscopically and microscopically for agglutination.

6. If agglutination is observed in any tube, it indicates incompatibility of blood of the donor and the recipient.

7. If there is no agglutination, incubate the tubes at 37°C for 60 minutes.

8. Centrifuge again and examine for agglutination as before.

9. If there is no agglutination, proceed with the albumin or antihuman globulin (AHG) serum technique.

Note

Incubation at 37°C in step 7 may detect some warm antibodies reacting in sa line which might have been missed at room temperature. For example antibodies of the P, MNSs or kell systems sometimes react this way.

Method 2: Albumin tube method

1. Label the tubes and mix the red cells and sera for major and minor crossmatch as for the saline method.

2. Incubate both the tubes at 37°C for 60 minutes.

3. Gently allow a drop of 22% bovine albumin solution to run down the sides of the tube so that it forms a layer between the cells and the serum. Do not shake.

4. Incubate at 37°C for 30 minutes.

5. Tap the tubes gently to disperse the cells and look for agglutination microscopically.

This albumin technique can detect some incompatibilities due to incomplete immune antibodies such as Rh-antibodies which may not be detected by the saline method.