posted on Sep, 4 2008 @ 06:23 PM
There are several possibilities:
1. They screwed up your original test. You're really type A
2. They only sort of screwed up your original test, you're a subgroup
of A which can test as type O, since the anti-A antisera may not
agglutinate with your subgroup type.
3. You got a transfusion. If you were type A but got a lot of type O blood (often given in an emergency) your own blood would be temporarily washed
out and you'd type a O for a short period.
You got a transfusion of bone marrow, type A and your original type has changed due to wbc engraftment. (rare, and unlikely, especially going from O
The most likely is the military screwed up and mis-typed you originally. It's not uncommon. In fact if you're going to be mis-typed the safest
"mistake" is to type you (wrongly) as type O since you'd only get type O blood, which is also compatible (as packed cells) to A, B and AB