As someone that works in a small blood collection facility, my first thought was how did this get through testing. Then I realized the problem is probably related to the antigens, not an antibody. First thing we check is DAT of the unit, which is negative. Then we would test against a couple of random samples from each compatible blood type, which you did. Then I would do a more elaborate ABO, which if there was a problem should have (in theory) been caught during testing. Then I thought about your reactions, 4+ tube, 2+ Gel, that's backwards from "normal" reactivity. Here we see a difference in reactions of at least one, usually two levels higher in Gel than tube. Unless whatever is happening is more IgM than IgG....... Then I think, do we all have Nabs that would react to some super low-incidence antigen? That was literally my thought process in 2 minutes, with no logical brakes. LOL. I'm not knowledgeable enough with this off the top of my head, so now it's time to read. Please post what the supplier says.