Weak or missing reactivity in cell grouping tests ("weak or missing antigens") involves unexpected reactions in the front cell group (Table 4-9). There are two main causes of weak or missing antigens.
| Examples | anti-A | anti-B | A1 cells | B cells | Tentative group | ||
|---|---|---|---|---|---|---|---|
| #1 | -- | -- | -- | 4+ | A | ||
| #2 | -- | 4+ | -- | -- | AB (or B*) | ||
| #3 | 1+ | -- | -- | 4+ | A |
* Also see Table 4-6 (weak or missing antibodies)
Weakened A Phenomenon Due to Leukemia
Examples #1, #2, and #3 could be examples of weakened A phenomenon. In Examples #1 and #2, the A antigen is totally missing, whereas in Example #3, the A antigen is only weakened (1+).
Mechanism/Cause: In some patients with leukemia the A antigen decreases in strength and may totally disappear for an unknown cause. It is believed that the leukemia causes the patients to stop producing N-acetyl-D-galactosaminyl transferase, the enzyme responsible for attaching GALNac (the terminal sugar of A antigen) to the H antigen substrate on red cells.
Examples #1 and #2 could be examples of an Am and AmB subgroup respectively. The subgroup is probably Am because it is one of the few subgroups of A that does not produce anti-A1. (Note: Example #3 could be group A3, particularly if MFA was present microscopically.)
To gain practice in solving ABO discrepancy problems and in recalling related information, see ABO Exercise "C"
|
| Weak or Missing Antigens |