Was the drug test a semi-routine toxicology screen, as they do in case people are either not telling them everything, unintelligible because the patient can only get out raccoon noises or there is no nurse on duty who speaks Sumerian or Old Norse, out cold, or out of their mind, for example, some beet-red guy screaming about the Stay-Puft Marshmallow Man and aliens from Uranus after washing down a whole Jimsonweed root and some Miltown-based PMS medication with some paint thinner? There would be no reason, in that case they are the hospital, not the KGB.
Do that at work, and the results will be different. From an accounting standpoint I cannot imagine any kind of drugs testing actually being cost effective, so the motives are a bit more open to interpretation, shall we say . . . oy vey