General Resolution Strategies for Subgroups

Failure to detect a weak subgroup of A or B may result in a patient or donor being mistyped as group O. Resolution strategies for recognizing and investigating subgroups include the following:

1. Use of the reverse serum group, which will usually detect discrepancies.

2. Use of anti-A,B which will detect some subgroups such as Ax.

3. Use of monoclonal anti-A and anti-B, which are very sensitive.

4. Reactions that are unexpectedly negative or much weaker than expected should be read microscopically to detect weak reactions or MFA.

5. Use of past records: the patient may be a known subgroup.

6. Secretor status testing (rarely done): secretors will sometimes (but not always) secrete H and either A or B antigens according to their group.

7. Absorption and elution studies: An absorption is a prolonged incubation of red cells with antisera in which the antibody in the antisera will adsorb or attach to the red cells if the corresponding antigen is present. An elution is a method to remove antibody from red cells. For example, to investigate a weak subgroup of A, the following could be done:
   1. Incubate the patient's cells with anti-A at 4(C. (anti-A reacts best at 4(C) for 1 - 4 hours, or overnight. If a small number of A antigens are present, anti-A will adsorb onto the red cells.
   2. Perform an elution on the adsorbed red cells to remove any antibody that has attached to them. Test the eluate against A₁ and O cells. If anti-A is present, only the A₁ cells will agglutinate, thus confirming that the A antigen must be present on the patient's cells.

8. Examination of the serological reaction patterns: each subgroup has a typical reaction pattern which gives a clue as to which subgroup it is.

General Resolution Strategies