The basic principle is that the fast remains valid and cannot be spoiled except by things for which there is Islamic religious evidence that they affect the fast.
In this case, there is no evidence that the fasting person breaks his fast because of this small amount of blood taken out for testing.
We rely on our generous community to create a lasting impact and ensure the continuous operations of your Masjid as the gathering place, school, and house of worship for Muslims across the Triangle.
Those who spend their wealth in charity day and night, secretly and openly—their reward is with their Lord, and there will be no fear for them, nor will they grieve.”
– The Holy Quran 2:274