With Pain Management, all patients (where I go for medical treatment) are required to consent to random drug testing. No consent, no treatment from the doc or his staff. Toxicology tests are run, and those do differ from "regular" blood testing.

The doc is looking for the presence of medications a patient is RX'd and also the absence of other drugs. If someone doesn't test "clean" or as s/he should, the doc will be having a serious talk with the patient. If RX'd meds are absent, it could be a possible sign of diversion.

If it's a comprehensive blood test, the results might possibly show elevation in certain things, which may catch a doctor's attention. The numbers would have to be higher than what the testing lab "sees" as the "norm."