I also give blood regularly, the last pint was for Howsie!
Blood donoring really wound me up a while ago.
I was diagnosed with a condition called polycythemia, which is an excess of red blood cells, causing a thickening of the blood. This can cause problems with the heart, and indeed I presented originally as the classic middle-aged, overweight businessman with chest pain.
The treatment is devastatingly simple - they extract a pint of blood, and flush it down the sink. At one point, they were doing this to me every fortnight, for about 2 years, then less frequently for another 3 years.
I asked if they couldn't use the blood, and they said "no".
I asked what was wrong with it - because the condition is not actually a blood problem, its to do with the bone marrow not turning off its red blood cell making process. The blood itself is fine.
They agreed that the blood was fine, and could be used, except policy said that blood extracted as part of a treatment had to be thrown away.
So there you go - over the years, they have extracted nearly 50 litres of blood from me, and flushed the lot.
Worse than HMRC!