What is Urine Toxicology?
Drugs of abuse testing is the detection of one or more illegal and/or prescribed substances in the urine, 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.
For most drugs of abuse testing, we 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. In addition, labs might perform testing for masking agents (adulterants). These may either interfere with testing or dilute a urine sample.
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. Positive screening tests are considered presumptive. 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) or liquid chromatography-tandem mass spectrometry (LC-MS/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, butalbital, amobarbital|
|Benzodiazepines||Diazepam, lorazepam, oxazepam, temazepam, alprazolam|
|Cocaine||Cocaine and/or its metabolite (benzoylecognine)|
|Methadone||Methadone, methadone metabolite (EDDP)|
|Opiates||Codeine, morphine, metabolite of heroin, oxycodone, oxymorphone, hydrocodone, hydromorphone|
Substances that are not similar to the defined classes can produce negative results even though they are present. 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), fentanyl, methadone, oxycodone (Oxycontin), meperedine, 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,” as part of a sports testing program, or to determine compliance with prescribed (pain) medications. 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 eliminate them from the body.
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.
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. Examples of false-positive screening results: Vicks nasal spray can test positive for amphetamines; poppy seeds can produce a false-positive for opiates. Prior to testing, make sure that the patient declares any medications that they have taken and/or for which they have prescriptions for so that results can be interpreted correctly.