Weak or Missing Reactivity in Cell Grouping Tests

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.

Table 4-9." 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)

  1. 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.

    Typical reaction pattern:

    Resolution:

  2. Weak Subgroups of A

    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.)

    Resolution:

Enrichment Activity 6

(available only to those enrolled in the DE course)

To gain practice in solving ABO discrepancy problems and in recalling related information, see ABO Exercise "C"


Weak or Missing Antigens

©1999 Division of Medical Laboratory Science
University of Alberta