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There is a way of confirming it by genoty[ing, but it would cost the Earth for very little return. I would like to know how old is the patient and what is the underlying pathology? You have to remember that the the A, B and H antigens, in common with other carbohydrate-based red cell antigens, are not direct gene products, simply because only proteins can be direct gene products, whilst sugars cannot. In the case of an AB individual, at least two different transferase enzymes are responsible for conferring either the N acetyl-D-galactoseamine residue, in the A antigen, or the D-galactose residue, in the case of the B antigen. These two enzymes are in direct competition with one another as to which one "wins the race" to convert the H backbone to either A or B; sometimes the "A transferase" wins, and sometimes the "B transferase" wins. In this case, it could be that the A-transferase is winning "hands down", and that the B-transferase is "whimping out a bit"! Sorry, that last bit wasn't written exactly scientifically, but I hope you understand what I mean!

I "grandfathered" the SBB exam 20 years ago. Not sure if it still works that way. I would think if you have all the right experience it should be possible.