Blood transfusion.
I am on the Anthony Nolan Bone Marrow register, but I don't know if it would affect that too.
When I went along to sign up for that, it took ages to find a vein (they are very recalcitrant), and the woman said "I'm not sure if they'll want you if it's that hard"- . Surely that can't be right? I mean, you can get blood eventually, although when I was allowed to give blood, more than once they had to abandon it because they didn't take the unit within the time limit, but it is possible, and if I were compatible, wouldn't they be drilling bone marrow out of my hip anyway?