In my life, I've given over eight gallons of blood. But for the last five or so years, I was on a “permanently deferred” list, for alternately failing and passing one of their precautionary blood tests.
Many medical tests are quantitative. You run a test that produces some sort of score, and people decide that a certain score is a pass or fail. They set the scores to minimize either false positives or false negatives, whichever is most awful. In the case of keeping the blood supply clean, false positives are less serious. The blood bank doctor who stopped me from giving blood was frank about this. My test was borderline, but two borderline fails and I was out.
About five years went by, and I passed the test yet again. I started thinking – after all this time, maybe the test has become more precise. I applied to the blood bank again to be allowed to give blood. The doctor agreed that the test had become more accurate and was happy to retest me one more time, and I passed.
Today was the glorious day when I went to the familiar blood room, and observed all the procedures that had stayed the same, and all the procedures that had changed. It was a triumph for me, but also a day of great nostalgia. I have only a few more years to give blood before I'm too old, but I might get to the ten gallon mark.
Here's one of the things that has changed since I last gave blood: Afterwards, the technician placed the usual bandage over the spot where she had drawn blood. She said “Be careful to bend your elbow as little as possible. There's no inflammation there now, but if you bend it a lot, there will be.”
I whined, “How do you remember not to bend your elbow?”
“Oh,” she said, “I just told you that to make me feel better.”