Drug testing is commonly a four-step process: collection, screening, confirmation, and review. When called in to take a drug test, the person being drug tested is met by a trained “collector,” or drug test administrator, who gives instructions and receives the specimen. It is also the collector’s job to complete the chain-of-custody form, which keeps track of where the specimen has been and who has handled it throughout the process. The form ensures that the specimen was handled properly and in such a way that does not call its source or the test results into question.

If the drug test requires a urine sample, If, a temperature strip is put on the collection container to guard against a substitute sample. A tamper-evident tape is put over the specimen container, and then the person being drug tested is asked to initial it and verify the chain-of-custody form.

Next, the specimen is screened for drugs or drug metabolites. If the screening test is positive, the test will be confirmed by a second, more exacting test. All confirmed positive tests should then be reviewed by a physician or nurse with knowledge of substance abuse disorders to rule out legitimate prescription drug use. Some specimens are screened at the collection site, and the initial results are known within minutes; others are screened at a laboratory. All negative screens—those that show no drugs or drug metabolites—are eliminated from further consideration.

Specimens that test positive for drugs in the initial screen are examined further in the laboratory through a second analytic technique called gas chromatography/mass spectrometry (GC/MS), which is actually a combination of two specialized techniques. Technicians use gas chromatography to separate the various substances in the specimen, then they make a positive identification through mass spectrometry.

A positive test result does not automatically mean the person uses illegal drugs. In fact, positive results are sometimes triggered by other, legal substances. Certain over-the-counter medications, for example, can cause a positive reading for amphetamines. So when the GC/MS confirmation test comes back positive, it is important for a doctor, nurse, or other specialist to review the results and determine if illicit drugs are indeed the culprit.