My whole family is more or less banned from giving blood. My parents were told outright not to come back anymore, because it was too much of a hassle to get too little blood; they had to use children's needles, because their veins are so small. With my brother, it was the same problem, and he passed out; they didn't actually say don't come back, but it was implied.
With me, they thought it was going to be different at first. When they pricked my finger to test (for diseases or blood type or whatever they test for), I bled a lot. When they tried to start taking blood, however, they couldn't find a vein. Once they finally did, they left me alone for ten or fifteen minutes, then decided it wasn't going fast enough and adjusted the needle. When they adjusted the needle, they hit the side of my vein, which caused it to bruise, so after another few minutes, they couldn't get any blood at all. I gave a little over a quarter of a bag. Again, the implication was please don't come back.
I can't give blood until June now anyway, since I got a tattoo last year. After that time is up, I might try again.
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"Nothing worth having is easy."
Three years!