What did she think they wanted the blood sample for?

Usually, the blood sample is taken early in the morning.

"All I need to do is take a small sample of your blood."

He took a sample of her blood, then left, saying that he'd have results for them in two hours.

It does not even include the taking of a blood sample.

"Want to give me a hand with the blood sample?"

There too men are being asked to give blood samples.

These tests usually can be done on the same blood sample.

Early in his stay, two medical students arrived to take a blood sample.

"I'm going to take a blood sample so we can figure out what kind of drugs he's been given."