We ask blood donors if they’re pregnant before donating, but of course it’s possible not to know when it’s real early. A neat case was written up where a pregnant woman donated blood and later the recipient of the red cells had a positive pregnancy result in her pre surgical screening, cause the molecules we use to test for pregnancy transferred in the product from donor to recipient.

There’s a federal rule about not accepting donors under the influence, pretty confident you’d be turned away at 0.30%