Known red cells are tested with the patient's serum in order to confirm the presence of the expected antibodies. This is called the reverse serum group or back group. It is always done (except on newborns), although it is only a check on the front group. The red cells used in the reverse group are A1 cells and B cells.
The front and reverse groups must agree with each other (Table 4-2). If they do not, a discrepancy exists which must be resolved. It is also important to note that reactions are typically strong, e.g., 3+ or 4+. Weaker than usual reactions are also considered as discrepancies. Defining discrepancies varies from lab to lab, e.g., some labs define discrepant results as those less than 1+ .
| Group | Front Cell Group (test for antigens) | Reverse Serum Group (test for antibodies) | |||
|---|---|---|---|---|---|
| anti-A,B (if done) | anti-A | anti-B | A1cells | B cells | |
| 1. B | 4+ | -- | 4+ | 4+ | -- |
| 2. A | 4+ | 4+ | -- | -- | 4+ |
| 3. O | -- | -- | -- | 4+ | 4+ |
| 4. AB | 4+ | 4+ | 4+ | -- | -- |
|
| Red Cells |