I guess it has something to do with blood being an organic material. It is no problem creating blood plasma (take 1 liter of distilled water, add 9 grams of salt, and voila, start your infusion). That's what it's made of, but it's not safe because the water surely has some germs in it, which would kill you sometime later. The white and red blood cells, that's the problem, because, as I already said, it is impossible to create organic material.
BAZL - Bundesamt gegen Zivilluftfahrt - royally screwing around with swiss aviation