Whoever has Blood taken from him while he is fasting
Question:
What is the ruling on whoever has blood taken from him while he is fasting during Ramadhan? The reason that this is done is for a blood test, and the blood is taken from his right arm. The amount that is taken is a moderate amount (in a syringe).
Answer:
The likes of this blood test do not corrupt the fast. Rather, it is pardoned because it is from that which there is a need for. It is not from the things that are known from the pure Islamic law to break the fast.
Shaykh `Abdul-`Azeez Bin Baz
Fatawa Islamiyah Page no. 275 Vol: 2