When testing a sample from a blood donor shows anti-A 0 and anti-B 0, which explanation fits best?

In the context of blood group serology, the presence of anti-A 0 and anti-B 0 suggests that there is no reactivity with A or B antigens when testing the donor sample with known anti-A and anti-B reagents. This finding aligns with certain rare subgroups of blood types, particularly those that might have altered expression of the A and B antigens.

A rare subgroup can have weakened antigen expressions or unique antigenic structures that may prevent standard reagents from detecting their corresponding antibodies. For instance, subgroups such as Ax or Ay may present with weak A antigen expressions, resulting in no observed reactivity with anti-A serum. Therefore, when both anti-A and anti-B show 0 reactivity, it is plausible that the donor belongs to a rare subgroup, as opposed to the blood group being undetermined or the sample being contaminated.

The possibility of contamination typically leads to inconsistencies or unexpected results in testing, while stating that the blood group is not yet determined would imply there is no information, which is not the case here since the non-reactivity can suggest specific subgroups. Moreover, if the individual had anti-A and anti-B in their serum, one would expect to see positive reactivity when testing against A and