Even if blood is infection‑free, it must still match the patient’s blood type. Giving the wrong blood can cause serious reactions, so matching is a critical safety step.

Basic matching: ABO and Rh

The first step is to know:

·       Your ABO group: A, B, AB, or O.

·       Your Rh type: positive (+) or negative (−).

Patients typically need blood that is compatible with their ABO and Rh type. For example:

·       Group A patients usually receive A or O red cells.

·       Group B patients usually receive B or O red cells.

·       Group O patients typically receive O red cells only.

·       Rh‑negative patients, especially women of child‑bearing age, are usually given Rh‑negative blood when possible.

This basic compatibility prevents strong, immediate immune reactions.

Antibody screening

Some patients develop additional antibodies against other red cell antigens (beyond ABO and Rh). This is more common if:

·       They have had many transfusions before.

·       They have been pregnant (as mothers are exposed to their baby’s blood group antigens).

The lab performs an antibody screen on the patient’s blood:

·       If extra antibodies are found, the blood bank searches for donor units lacking those antigens.

·       This may require using special donor registries or rare donor databases.

Cross‑matching: final compatibility check

Cross‑matching is like a final rehearsal before the real transfusion:

1.      A small amount of the patient’s blood is mixed with a small amount from the donor unit in the lab.

2.     The mixture is observed for signs that the patient’s antibodies are attacking the donor red cells (clumping or destruction).

3.     If no reaction is seen, the unit is considered compatible.

If there is a reaction, that donor unit cannot be used for that patient, and another unit must be selected.

Bedside checks before transfusion

Even after all these lab tests, there is one more safety layer: bedside checking.

·       Two staff members usually confirm the patient’s identity (name, ID number) and match it with the label on the blood bag.

·       They verify the product type (red cells, platelets, plasma), blood group, and expiry date.

·       Only when everything matches do they start the transfusion.

This combination of blood group testing, antibody screening, lab cross‑matching and bedside identity checks makes serious compatibility errors extremely rare.