Oh, that's just for piss. For blood, any amount is undetectable in a few day, no matter what anyone tells you. Hair I'm not too sure about I hear it's something like if you smoked like 3 times within the past i forget how many months it will show up. There are methods, though, to help clear it out of your hair, but I don't know much about them.
Mostly companies will never blood tests. Some hair test. Most piss test. Piss is the easiest to cheat on too but it doesn't sound like you will need to.