Testing for drugs of abuse or “drugs of abuse screening” is the detection of the presence of both legal and illegal substances. Drug testing is used for many purposes including clinical or medical care, workplace testing, postmortem (cause-of-death), corrections and other law enforcement, and sports testing. Each reason for testing has its own requirements regarding which drugs to include in the test, how fast the results are needed, and how specific (what drugs are detected by the test) and sensitive (what is the lowest amount detected) the test must be. In addition, for some types of testing (for example, workplace testing of federal employees) there are many regulations that cover the test from collection through interpretation and reporting of results. It is important for the ordering physician, law enforcement representative, forensic professional, government entity, insurance agent, employer, and sports organization as well as for the person being tested to understand what exactly is included in the testing, how it is done, and how the results may or may not be interpreted. This process is not nearly as simple or straightforward as collecting a sample and requesting that it be tested for “drugs.”

How is it done?

Testing for drugs of abuse (and other drugs) is done differently, depending on the application. In workplace testing, sports testing, and some clinical testing programs, it is important to know the actual drug or drugs present, and testing is a two-step process consisting of a screen, followed by confirmation of any positives. Confirmation may not be done in certain clinical situations but may be requested by the physician as follow-up. False positive and false negative results can occur at the initial screening stage. Therefore, taking any action based solely on a screening result may be problematic. Most laboratories use commercially available tests that have been developed and optimized to screen for the “major drugs of abuse.” Screen in this context means a preliminary result. Each screen is for a different drug or drug class such as amphetamines, barbiturates, benzodiazepines, cannabinoids, cocaine, opiates, and phencyclidine (PCP). Patient/donor results are compared with a predetermined cut-off. Anything below that cut-off is considered negative. Depending on the reason for the test, specimens giving a result above the cut-off may be confirmed with a more specific test. In the confirmation test, the exact substance present is identified with a very sensitive and specific method, such as gas chromatography/mass spectrometry (GC/MS).

Some of the “club drugs,” such as methylenedioxy-methamphetamine (MDMA, Ecstasy) and flunitrazepam (rohypnol, date-rape drug) may be difficult to detect, either because available assays do not always detect the drug (Ecstasy) or the drug does not remain in the body long enough to be detected (gamma-hydroxybutyrate, GHB).

Samples Used/Drug Matrices
Urine is the most frequently tested sample, but other body samples (matrices) also may be used for drug abuse screening. Hair, saliva, sweat, and blood are used but not interchangeably with urine. Drug compounds in these other matrices are primarily the parent (original) drugs, not metabolites, and they reflect a different “window” (time period) of drug use. Urine testing shows drug use over the last 2 or 3 days for amphetamines, cocaine, and opiates (an exception is marijuana (cannabinoids), which may be detectable for several weeks). Hair samples, which test the root end of the hair, reflect drug use within the last 2 to 3 months but not the most recent 2-3 weeks (the amount of time it takes for the hair to grow). Saliva shows which drugs have been used in the last 24 hours, and sweat, which is collected by wearing a patch, gives a time-averaged representation. These other matrices are often used for specific purposes. For instance, hair samples may be used as an alternative to urine testing for pre-employment drug testing. Sweat testing may be used as a court-ordered monitoring tool in those who have been convicted of drug use, while saliva is often used by the insurance industry to test insurance applicants for cocaine use. Blood is most frequently used for alcohol testing.