One is allowed to donate blood in exigent and extreme states. This ruling has been compared with that of milk i.e. as it is lawful for a mother to breastfeed her child in the time of need, in the same way it is allowable to donate the blood at the time of extreme compulsion.
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.