Does having a blood test interfere with fasting?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Taking a little blood for tests does not affect the validity of fasting, neither does donating blood. This is the most preponderant opinion of Muslim scholars. They compare donating blood to the ruling of Hijaamah (cupping) which does not affect the validity of fasting.

Allah knows best.