Urine drug screening

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Definition

Urine drug screening, or toxicological screening, is a process of chemical analysis designed to test patients for drug abuse, or to insure that a patient is substance-free before undergoing a medical procedure.

Description

Urine drug screening can be used to evaluate possible accidental or intentional overdose or poisoning, to assess the type and amount of prescribed and/or illicit drugs used by a person, or to determine the cause of acute drug toxicity. It is also used to monitor drug dependency or to determine the presence of drugs in the body for medical and legal purposes.

In many occupations, urine drug screening has become a required condition of employment. Nearly all workers in certain occupations, such as law enforcement and transportation, must submit to periodic, random, and post-incident drug screening. Federal laws mandate the administration of drug screens to workers in the transportation industry, including bus drivers, truckers, airline employees, and railroad workers. Federally required testing must be conducted by a laboratory certified by the Substance Abuse and Mental Health Services Administration. Other industries must follow state regulations, which vary considerably.

Urine screening tests are able to detect general classes of compounds, such as amphetamines , barbiturates , benzodiazepines, and opiates. Drug screening can also detect cocaine, marijuana, and phencyclidine (PCP). The screening tests themselves are unable to distinguish between illicit and prescription drugs within the same class. A patient taking prescribed codeine pills and an individual using heroin would both show positive urine screening tests for opiates. It is also possible for some over-the-counter medications to cause a positive drug screen in someone who has taken neither illegal nor prescription drugs. These incorrect reactions are known as "false-positives."

Urine drug screens can detect the use of several drugs. Some of these drugs are as follows:

cocaine
amphetamines
heroin
morphine
phencyclidine (PCP)
benzodiazepines
alcohol
hydromorphone
tetrahydrocannabinol (THC)
propoxyphene
methadone
codeine
barbituates

Certain foods, such as poppy seeds, may result in a positive urine screen for opiates, since poppy seeds are derived from opium poppies. Preliminary urine screening results, when positive, should be confirmed by a more accurate method that can distinguish between poppy seed ingestion and use of heroin or other opiates. Poppy seeds and opiates produce different chemicals, known as metabolic breakdown products or metabolites, as they travel through the body, allowing them to be distinguished from one another.

Sample collection

The method of collecting a urine sample for drug screening can be important. Some illicit drug users may attempt to substitute another person's urine, or chemically alter their own specimen. If the urine drug screen is being used for an important decision, such as employment or legal action, procedures to minimize chances of an adulterated or substituted sample may be necessary. These include measuring the temperature or pH of the sample immediately after it is procured, and using tamper-proof containers. Supervised specimen collection may be conducted to ensure that the urine indeed comes from the person being screened.

The most commonly used method for urine drug screening is immunoassay, a rapid and accurate test that uses antibodies embedded on test strips to reveal drug use. Antibodies react only in the presence of very specific substances—in this case, drugs present in urine. When a sufficient concentration of a drug (or drugs) are present, the test strip will indicate which substances have been detected. A control band on each strip confirms that the test was done correctly.

Positive screening results should always be confirmed by a more sensitive method. The most widely accepted corroborative test for all drugs is gas chromatography/mass spectrometry (GC/MS), which can determine the specific substances in the body by recognizing not only the molecular structure of the original compound, but also its metabolite, a chemical created when the drug is metabolized.

Resources

BOOKS

Kaplan, Harold, MD, and Benjamin J. Sadock, MD. Synopsis of Psychiatry. 8th edition. Philadelphia: Lippincott Williams and Wilkins, 1998.

PERIODICALS

Persoon, Thomas, MS. "Virtual Hospital: Clinical Laboratory Improvement Act: Therapeutic Drug Monitoring and Drug Abuse Screening, IV." Screening for Drugs of Abuse. The University of Iowa, 1999.

Policy Statement: Drug and Alcohol Screening. American Academy of child and Adolescent Psychiatry, Approved by Council, October 1990.

Barbara S. Sternberg, Ph.D.