Assalam o alekum.During the swan (roza) time can give 10ml blood to HIV test.
بسم الله الرحمن الرحيم
(Fatwa: 1496/1496/M=1431)
Blood donation does not nullify the fast. One can give blood at the time of need and compulsion.
Allah knows Best!
Darul Ifta,
Darul Uloom Deoband