Dr. Hussam al-Din ibn Musa Afanah – professor of jurisprudence and Usool – Al-Quds University, Palestine says:

Donating blood is a necessary thing for human beings, I do not exaggerate if I say that its ruling is fard kifaaya (if some have done it, the sin is waived for the rest.) This is as a result of wanting to save the sick and the injured from various accidents. Thus, it is necessary for a person to donate blood for Allah’s sake without asking for anything in return after the donation so as to save the life of the person who needs it.

It is not permissible to take compensation for the blood expended because humans are honored, and it is not permissible to trade any part of the body. So it is not permissible to sell, say his hair, as animal wool are sold, let alone sell his blood as such trade is not permissible. Allah says: “And we have certainly honored the children of Adam…” Q17:70. Therefore, in taking this honor, it is not appropriate for man to trade his parts of the body as goods are being traded.

If it is not possible for a person in need of blood to obtain blood as a donation or a gift except through purchase, then it is permissible for such person to buy the blood. However, the sin is on the one who collected the money not the one who donated the blood. 

It should be mentioned here that blood transfusion has nothing to do with spread of sanctity between the recipient and giver, as is the case of breastfeeding.