Group O or weak subgroup of A?

[Learning from the experts 5]

Donor

Forward group: -A:0, -B:0, -A,B:0

Reverse group: A1C:0, A2C:0, BC:4

Cold panel at IS, RT, and 4C with O, A1 and A2 cells: 1+ reactions with A1 cells only

Adsorption elution with polyclonal anti-A: no evidence of A antigen

What next? Geno?

Why there are no reactions with A2 cells?

 

[Malcolm Needs ★ 4,910]

Essentially, this is because the A1 antigen is qualitatively different from any other A antigen.  As a consequence, all individuals with an A subgroup of any kind are capable of producing an anti-A1, which would explain the reaction with A1 cells, but not A2 cells.  In addition, the different A types, including, in this case, A1, are, in effect, a continuum from the strongest A1, right down to the weakest, for example, Am, and, in some cases it is impossible to detect any A antigen on the red cells, but it is possible to detect A substance in, for example, saliva, which would explain the results of the adsorption/elution testing.

I really would advise against ABO genotyping, unless you are really interested (and I wouldn't blame you if you were), as it is a very expensive technique which won't tell you in which "pool" to put the donor (A or O).  This will still be subjective.

If it is just that you are concerned that this patient could be "dangerous", in theory they probably could be (although, in practice, probably not so) and I would enthusiastically thank the donor for giving, but with an explanation detailed enough to let them know why (not over-burdening them with science, while also not treating them as an idiot), ask them not to donate again in future.

[Learning from the experts 5]

Thanks, Malcolm! We will probably defer the donor. I had the same explanation in mind but my colleagues were telling me that it's a group O donor while I thought it's a weak subgroup of A with anti-A1.

[mrmic 55]

I apologize for such a late comment for this topic and possibly bringing up minor point regarding this typing.  I'm sure that the probability that the reactivity with the A1  red cells was confirmed by testing other sources of A1 red cells to rule out the possibility of a antigen of low frequency on the initial A1 red cells tested.  I just did not see this mentioned in the comments.  The blood center where I had worked took deferring donors very seriously as it affects the blood supply and the donor's altruism.   Mr. Needs response and explanation of A subgroups is excellent and I always appreciate his ability to provide informative and education responses to this forum! I agree completely with his comments on A1 subgroups and speaking with the donor about the test results and whatever you decide to do with his/her future donations.