Switched at birth? Different blood type than parents.

It’s entirely possible however extremely unlikely. As mentioned already, it’s possible that you’re Rh null or Bombay phenotype and the type of testing used didn’t pick this up. I’d wager however that they’ve used serology testing as most referencing laboratories would do. If we also discard the possibility of random mutation and work only with standard genetics, then the possibility of two A+ parents having an O+ child is around 6.25%.

Given that A is a dominant allele, your parents possible genotypes could have been AA or AO so it’s entirely possible that you received the O allele from both parents, giving you blood group O. Rhesus inheritance is entirely separate from ABO inheritance but that’s not even the question.

Yes it’s possible that both of your A+ policies parents have an O+ child.

/r/genetics Thread