The Test Sample
What is being tested?
Drugs of abuse testing is the detection of one or more illegal and/or legal substances in the urine or, more rarely, in the blood, saliva, hair, or sweat. Testing detects substances not normally found in the body, with the exception of some hormones and steroids measured as part of sports testing.
Drugs of abuse testing usually involves an initial screening test followed by a second test that identifies and/or confirms the presence of a drug or drugs. Most laboratories use commercially available tests that have been developed and optimized to screen urine for the "major drugs of abuse."
For most drugs of abuse testing, laboratories compare results of initial screening with a predetermined cut-off. Anything below that cut-off is considered negative; anything above is considered a positive screening result.
Among drugs of abuse, each class of drug may contain a variety of chemically similar substances. Legal substances that are chemically similar to illegal ones can produce a positive screening result. Therefore, screening tests that are positive for one or more classes of drugs are frequently confirmed with a secondary test that identifies the exact substance present using a very sensitive and specific method, such as gas chromatography/mass spectrometry (GC/MS).
Some of the most commonly screened drug classes are listed in the table below.
|Drug class screened||Examples of specific drugs identified during confirmation|
|Barbiturates||Phenobarbital, secobarbital, pentobarbital|
|Cocaine||Cocaine and/or its metabolite (benzoylecognine)|
|Opiates||Codeine, morphine, metabolite of heroin|
(See a more comprehensive list of drug classes and drugs of abuse.)
Substances that are not similar to the defined classes can produce false-negative results. Some drugs may be difficult to detect with the standardized assays, either because the test is not set up to detect the drug, such as methylenedioxy-methamphetamine (MDMA, also known as Ecstasy or Molly), oxycodone (Oxycontin), or buprenorphine, or because the drug does not remain in the body long enough to be detected, such as gamma-hydroxybutyrate (GHB).
For sports testing of hormones and steroids, each test performed is usually specific for a single substance and may be quantitative. Athletes, especially those at the national and international levels, are tested for illegal drugs and are additionally prohibited from using a long list of substances called "performance enhancers."
Groups of drug tests are typically ordered for medical or legal reasons, as part of a "drug-free workplace" or as part of a sports testing program. People who use these substances ingest, inhale, smoke, or inject them into their bodies. How much of these drugs the body absorbs and their effects depend on the substances, how they interact, their purity and strength, their quantity, timing and method of intake, and an individual's ability to metabolize and excrete them.
Some drugs can interfere with the action or metabolism of other medications, or have additive effects, as in the case of taking two drugs that both depress the central nervous system (CNS). Drugs may also have competing effects, as can happen when one drug that depresses the CNS and another that stimulates it are taken.
How is the sample collected for testing?
Urine is the most frequently tested sample in drug abuse screening. Other body samples, such as hair, saliva, sweat, and blood, also may be used but not interchangeably with urine.
Urine and saliva are collected in clean containers. A blood sample is obtained by inserting a needle into a vein in the arm. Hair is cut close to the scalp to collect a sample. A sweat sample is typically collected by applying a patch to the skin for a specified period of time.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
Certain prescription and over-the-counter drugs may give a positive screening result. Prior to testing, you should declare any medications that you have taken and/or for which you have prescriptions so that your results can be interpreted correctly.