Human beings are honourable with all their organs. Almighty Allah has given us all these parts as a trust and we are not their owner. Hence it is not lawful for us to sell any of our organs or gift it. However, the scholars of Fiqh have allowed to donate the blood in severe compulsion when blood is not available and life of patient is in danger then it is allowable to donate blood in order to save the life.
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.