❖ Question:
Is it permissible to donate blood during the day in Ramadan, or does it invalidate the fast?❖ Answer:
If a person donates a large amount of blood—such as when blood is drawn from the veins to save a patient’s life or for emergency storage purposes—then, by analogy to ḥijāmah (cupping), the fast becomes invalid.However, if only a small amount of blood is extracted—such as through a needle or slide for testing purposes—then this does not break the fast.
— Shaykh Ibn Jibreen رحمه الله