I agreed to give blood at the church blood drive, since I don't have a race coming up soon. However, I expected to get refused for low hemoglobin, as that has happened to me about half the time and the timing wasn't good. To my surprise, I was able to give. Apparently I've got the iron I take right--a brand called Slow-Fe, every day for a few days when most needed and once or twice a week the rest of the month.
Since I haven't given in at least two years it is now a bit of an experiment to see how much effect giving blood has on my running and swimming (and biking, but I expect less effect there). It may also make my blood sugar harder to control; I saw such an effect the last time I gave and also when I spent several days high altitude. My theory was that my body thinks I needed higher blood glucose when working hard to make more red blood cells. But my diabetes has definitely gotten easier to control in the last year, so maybe I won't see that effect so clearly.
At least they did a good job of sticking me--success on the first try. When I had some tests at the hospital a couple of years ago three different technicians tried to get an IV going. The third one was the expert they call when they have trouble, and it took her several tries.