For Kemetic religion it's an interesting conundrum. It wasn't considered in antiquity, since obviously it was impossible.
If you look at ancient practice and beliefs, there are some concerns: As opposed to other cults, Egyptians didn't consider blood to be a very sacred thing. Blood was not spilled in offering for the gods. It was instead an impure liquid, one that belongs inside the body only.
Body parts of a human were considered important for the afterlife, so by logic, you'd try to keep your body whole even in death.
However, I am personally in favor of any type of voluntary donation.
The importance of helping other people is stronger than any spiritual concern, as the spiritual points can simply be rectified with magic:
So what if a corpse is incomplete - you can use magical substitutes or a Ka-statue instead.
So what if blood is impure or may carry traces of the donor's personality - you can just do a purification rite after receiving a transfusion.
So what if donating makes you bleed and causes a wound - it will heal, and you can purify.