You are supposed to pass your drug test so don't expect a ticker tape parade. It takes about 3-5 business days to get results so if you pass you will hear back from the employer you're cleared for landing. If you fail you will usually hear from the MRO who is a M.D. who reviews test results and checks to make sure all procedures were followed.

Edit: You posted while I was writing. 95% chance you either have a dilute negative or you are positive for something if they are calling you.