Legal Question

In routine physical exams, one is asked if one consumes illicit substances. I always respond "no" to this question lest my premiums may rise if I answer honestly. But let's say I am required to take a piss test for chlamydia & gonorrhea. What would be the lawfulness of the lab subjecting my urine specimen, which I submitted for a chlamydia & gonorrhea test, to a drug test? This is something I have wondered for a long time, so any reliable answers will be greatly appreciated.

The lab cannot test the sample for drugs unless it has been authorized by the client that is paying for the test.