Transfusion services always:

1.      Test the donor’s ABO and Rh group.

2.     Test the patient’s ABO and Rh group.

3.     Perform cross‑matching, where a sample of the patient’s blood is mixed with the donor’s blood in the lab to check for reactions.

If there is any sign of incompatibility, that unit is not used for that patient.

Some quick compatibility examples (for red cells):

·       Group O negative: often called a “universal donor” for red cells because it lacks A, B and Rh D antigens.

·       Group AB positive: often called a “universal recipient” for red cells, because such patients have no anti‑A, anti‑B or anti‑D antibodies.

However, in practice, blood banks always try to give type‑identical or closely compatible blood, not just rely on “universal” types. That is why having a broad pool of voluntary donors of all blood groups is so important for a country like Pakistan.