The Jewish ultra-Orthodox concern with blood infusions is in part superfluous. Jews are enjoined against consuming animal blood, “for its soul is in its blood.” Soul, however, can be only in a single place at a time, and it’s either in the animal or in its blood. The commandment, therefore, only deals with slain animals and leaves open the possibility of drawing blood from live animals and humans.

blood transfusion in Judaism

There is an adjoining prohibition against cutting the flesh of a living animal. Blood, however, is not flesh: we’re allowed to eat an animal’s flesh but not to drink its blood. In light of the “soul-blood” commandment, we can plausibly infer that there is a prohibition against shedding the blood of a living animal before it dies. It is doubtful whether we can extend the prohibition of cutting flesh to prohibit all animal suffering; doubtlessly, a sheared sheep suffers considerably, but shearing is not regulated. Perhaps it is prohibited to inflict enormous, death-like suffering only.

Drawing the blood of live humans and animals by medical means doesn’t cause them considerable suffering or cause their death, so is not prohibited.

Perhaps blood consumption is prohibited per se, regardless of the blood’s source? The mandate of capital punishment for intercourse with a menstruating women suggests such a broad assumption.
A contrary argument, that priests and arguably medical professionals, though in constant contact with blood, incur no guilt on its account, would be wrong. They derive no personal benefit from the blood and are not culpable. True, doctors receive payment for their services, but the payment is for healing; the contact with blood remains incidental.

The blood of menstruation, however, is considered to be from a wound, and therefore symbolic of death. Plausibly, blood that is not related to wounding and death, such as blood drawn for an infusion, lacks the stigma.

There is also an argument of necessity. An animal slaughterer comes into contact with blood, but is not guilty because the contact is unavoidable. Blood transfusions in life-threatening circumstances can be justified by similar necessity as that which makes us slaughter animals to eat and live ourselves.

The example of a woman in childbirth is instructive. During birth, she becomes unclean through contact with the blood of the wound, and is instructed thereafter to purify herself by moderate sacrifices. I lean to the opinion that blood transfusions from living humans and animals is possible, but leads to the receiving party’s ritual impurity.