I went to give blood yesterday evening. The last time I tried, I was disqualified as my haemoglobin level was slightly too low. This time I didn't even get as far as having my haemoglobin measured: I was disqualified on a technicality. I don't know what the procedure is like in other countries, but here first one fills out a questionnaire, then a medic (?) goes over the questionnaire and checks answers, then one's blood pressure and haemoglobin level is measured. One is permitted to give blood only if the two checking stations give their permission.
The questionnaire contains all manner of personal details, including visits abroad, previous illnesses, sexual practices (I used to comment that homosexuality is banned whereas bestiality is fine - because there's no question about sex with animals), medication, etc. Some of these questions are designed to save the donor from problems and some are designed to obtain 'good' blood. It often seems that despite the desire to obtain as many blood donations as possible, there is a counter-intention to block as many 'inferior' donations as possible (my term). One question asks about invasive procedures in the past six months: as I had an endoscopy two months ago with biopsy, I am disqualified.
It doesn't matter that the endoscopy and the biopsy showed that everything is ok; the biopsy is performed with a utensil which is used many times (although obviously being sterilised between patients) and so is a no-no for the ultra strict requirements of blood donation.
I decided several years ago that I would stop even trying to donate blood after two successive rejections. Well, those two rejections have now occurred and so I recuse myself from ever giving blood again.
In this case, something trumps altruism.