ABO grouping consists of:
● Cell grouping in which the red cells are tested for antigens A and B using anti-A and anti-B sera.
● Serum grouping (reverse grouping) in which the serum is tested for anti-A and anti-B antibodies using known A and B red cells.
Why perform both cell and serum grouping ?
- It greatly reduces the risk of errors in ABO grouping (serves as a double check).
- There is less risk of misgrouping a group A person with weak antigen A as group O (or group AB as group B) because the error will be detected when serum grouping.
- Errors due to autoagglutination will also be detected more easily.
- Serum grouping using a tube will also detect the presence of anti-A and anti-B haemolysins in group O donor blood.
Grouping infants and elderly patients
Serum grouping is not performed when grouping infants below 4 months of age because naturally occurring anti-A and anti-B antibodies are only formed 3–4 months after birth.
When ABO grouping elderly people or persons with a gamma globulin deficiency, anti-A and anti-B may react weakly in the serum group and therefore cell grouping will be more reliable.
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