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 ★ 4,278]

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.