From another site re donating blood: Do NOT donate blood unless asked to... When 9/11 happened, they had a huge influx of blood, much of which wasn't needed. They then had a dip, as people can't donate blood again for (6 months?) The end result was a lot of wasted blood, and the struggling to fulfill supply. The blood service will make an appeal if neccesary. Also, please don't take my post as patronising or condescending, just trying to point it out..