See the topic posted by cofty on the sacredness of blood and the discussions posted on that thread.
One interesting point is that when an Israelite ate a dead animal that died of natural causes, he was not bloodguilty for doing so. Therefore, what about taking a pint of blood from an animal or human without killing anybody and consuming the blood putting it into a person’s vein for medical reasons, is such blood sacred to God or is it the same as that of a dead animal?