What is the ruling on blood transfusion?

It is permissible to transfuse blood to a sick or injured person if their life depends on it, due to the absence of a permissible alternative. This falls under the category of necessary sustenance. It is permissible to transfuse blood from a donor if it does not result in excessive harm to them. Reliance in this matter is placed on the opinion of a Muslim physician, and if that is not possible, it is permissible to rely on the opinion of a non-Muslim physician who is expert and trustworthy. It is permissible to donate blood when there is a need, and it is permissible to establish Islamic blood banks to store blood and assist those in need without financial charge, for the general welfare of Muslims.