Compatibility Testing

When patient requires transfusion or blood on standby, compatibility testing will have to be done.
There are 2 kinds of compatibility testing. Namely, Abbreviated crossmatch (AXM) or extended crossmatch (EXM)

Extended crossmatch will have to be performed when:
1) patient has history of significant red cell Ab
2)Ab screening is positive
3)Patient has a recent episode of adverse transfusion reaction
4)Patient is <4 months old

AXM is performed when patient all 4 EXM criteria does not apply to patient.

For EXM, there are 3 phases. Namely the saline phase, LISS phase and AHG phase.

Saline Phase
1) Add 3d patient serum
2) add 1d 3-5% washed donor cells
3)incubate for 20mins at room temperature
4)Spin down at 1000rpm for 15secs and read
Check for haemolysis and then re-suspend and read under microscope for agglutination.

LISS Phase
1) Add 3d patient serum
2) add 1d 3-5% washed donor cells
3) Add 2d LISS. Mix well
4)incubate for 10mins at 37 degree celcius
5)Spin down at 1000rpm for 15secs and read
Check for haemolysis and then re-suspend and read under microscope for agglutination.
Then we'll proceed to AHG phase

AHG Phase
1) Wash the cells in the LISS tube in 0.9% saline 3 times.
2)Add 2d AHG to the red cell button in test tube
3)Spin down at 1000rpm for 15secs and read
4)re-suspend and read under microscope for agglutination.
If the tube gives negative results, add 1d control cells and then spin again. Should it yield negative results again, test will have to be repeated.


For AXM, these are the steps. It's much easier and takes a shorter time
AXM
1)Label 1 tube for the donor sample to be tested.
2) Wash this donor sample in 0.9% saline.
3)Add 2 drops of patient serum to a clean, labelled tube
4)Add 1 drop of 3-5% washed donor cells to the labelled tube
5)Spin down at 1000rpm for 15secs and read
6)Check for haemolysis and then re-suspend and read under microscope for agglutination.

Purpose of compatibility testing is to select a unit of compatible blood for each potential recipient which will have acceptable survival and will not cause clinically significant destruction of the recipient's own cells. As long as it's possible, units of the same blood group and Rh(D) group will have to be selected for patient.

Since EXM consist of 3 phases, and includes incubation at 37deg, it can better detect IgG antibodies .

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