What is the ruling on cupping and blood transfusions while fasting?
The majority of scholars have maintained that cupping does not vitiate fasting because only those things which enter the body invalidate the fast and not those which exit it. Blood transfusions have the same ruling; they do not invalidate the fast provided they do not harm the person fasting or have a debilitating effect. And God Almighty knows best.
Dar al-Fatwa al-Misriyya