The amount of blood they take is negligible. A healthy person regenerates the amount lost in less than half an hour. One famous UFC fighter has a blood test taken after every round of sparring when he's training for a fight to monitor lactic acid levels.

It depends on your definition of "inasive". If somebody following you round until you've got enough pee to fill a container is invasive then it's invasive. But if you've been accused of being a cheat and you want to clear your name to the world then it's fuck all.