Drug Tests: Don't Fall Victim to a "False-Positive"
A 17-year-old gymnast was stripped of her gold medal in the 2000 Olympics because she tested positive for drugs. But she said that all she took were two cold tablets provided by her doctor. Here's what you need to know about drug testing and how to prevent false-positives caused by "hidden" substances.
Drug Testing in the Workplace
Random drug testing is becoming increasingly popular in the workplace. Airline, railroad, trucking, pipeline, mass transit, and shipping industries do drug tests under US government mandate.
Private companies conduct drug testing to keep health insurance costs down, improve employee productivity, decrease absenteeism, and ensure a safe work environment.
A positive drug test is cause for dismissal in many companies. Most companies that drug test do not hire job candidates who test positive.
Drug Testing in Schools
Drug testing is also becoming more common in schools. There has been a steady increase in the number of private schools using drug testing as a prerequisite for admittance or for participation in athletics or extracurricular activities.
What Are They Testing For?
The most common substances being tested for include the following:
Other substances that may be tested for include:
- ]]>Prescription-type stimulant]]>, sedative, tranquilizer, or analgesic used for nonmedical reasons
- ]]>Heavy alcohol use]]> (defined by the US government as drinking at least five alcoholic beverages in one day, five times per month)
- Hallucinogenic drugs (LSD, Peyote, Mescaline, Psilocybin, and Ecstasy)
- Inhalants (fumes or gases that are inhaled to produce intoxication such as glues, aerosols, butane, ether, nitrous oxide, and solvents)
- Anabolic steroids
Types of Drug Tests
Urine testing is the most popular type of test because it is simple, noninvasive, and highly accurate. A component of marijuana called THC can be detected in the urine 3-30 days after marijuana is smoked. Most other drugs can be detected up to 2-4 days after use. Anabolic steroids can be detected up to 14 days after use.
Many techniques are used in an attempt to cheat on a urine test. Attempts have been made to dilute the urine with tap water, substitute a clean urine sample from another person, or spike the sample with chemicals to produce a false-negative.
Testing labs combat these problems in the following ways:
- Removing sinks from restrooms in testing facilities
- Watching or listening to the person providing the urine sample
- Checking the color, temperature, pH, specific gravity, and creatinine levels of the urine to determine if it has been diluted
Urine drug testing is widely used for testing for opioids and illicit drugs. In the majority of situations, a screening test is used that utilizes an immunoassay, which detects the parent drug and/or metabolite. It usually tests for marijuana, cocaine, opiates, PCP, and amphetamines. Typically, the screening immunoassay detects the amount of drug present in urine above a predetermined "cutoff" concentration. Thus, a substance may be present, but if the concentration of that drug is below the "cutoff," the result will be negative. For more precise results, the confirmatory urine drug test is done by gas chromatography/mass spectrometry or high-performance liquid chromatography. This test is highly specific and is typically used when testing for the presence of a specific drug is needed.
Hair tests are less susceptible to adulteration than urine tests. Hair provides a semi-permanent record of drug use. Drugs circulating throughout the body cling to the hair as it grows. Therefore, if the drug was taken recently, it will be found in hair near the scalp. If the drug was taken in the past, the drug will be found in hair that has grown out.
Typically, drugs cannot be washed out of the hair. This is in contrast to drugs in smoke, which stick to the hair and can be removed with shampoo. However, products used on the hair might, at times, interfere with test accuracy.
Hair testing has an advantage because it can detect drug use over longer periods of time (usually around 90 days). This test is available for home use.
To test sweat, a bandage-like patch is placed on the upper arm, midriff, or lower back and worn for at least 24 hours to collect sweat. Contaminants from the environment cannot penetrate the adhesive barrier from the outside, so the patch can be worn during normal activities, including bathing and swimming. To prevent tampering, the adhesive plastic film cannot be reapplied once removed. The results cannot be diluted.
Residue tests are typically found in home testing kits that allow parents to test their children. The kit comes with a pad that picks up drug residue by swiping the pad on the child's belongings. The pad then is mailed to the manufacturer for testing. The major flaw with this test is that it cannot determine whether any drug residue found was left by the child under suspicion or by someone else.
Blood tests are the most accurate test, but are not used routinely in the workplace.
A saliva test is a way to detect if someone has been using drugs within the past few days. This type of test can detect many illegal substances, such as heroin and cocaine; but, it may be less reliable in detecting marijuana.
This involves exhaling into a hand-held machine tests for alcohol consumption. Devices are available for home use. There are also disposable devices.
In some cases, a drug test may report the presence of illicit drugs, although none were taken. While the rate of such “false positives” has gone down in recent years, it is still significant. Lab errors account for some of the mistakes, but most false-positives may be attributed to more than 300 over-the-counter drugs and foods that can affect the test (see table).
|If you take or eat:||You could test positive for:|
|Ibuprofen (common pain reliever)||Marijuana, barbiturates, or benzodiazepines|
|Hay fever remedies||Amphetamine|
|DHEA (dehydroepiandrosterone )||Anabolic steroids|
|Novocaine (used in dentistry)||Cocaine|
|Dietary supplements containing ephedrine||Amphetamine|
|Hemp food products**||Marijuana|
*Large amounts of poppy seeds—for example, a pastry filled with poppy seeds, not a poppy seed bagel—would need to be consumed to cause a positive test. However, sophisticated testing can discern poppy seeds from opiates.
**Hemp oil is eaten for its supposed nutritional benefits.
If you are mistakenly found positive for drug use, evaluate whether you have taken any substances known to cause false-positives. Also, remember that liver or kidney problems, may cause a false-positive with some testing methods.
National Institute on Drug Abuse
US Food and Drug Administration
Public Health Agency of Canada
Gourlay D, Heit H, Caplan Y. Urine Drug Testing in Primary Care: Dispelling the Myths and Designing Strategies. Monograph PharmaCom Group, Inc; 2002.
Reisfield GM, Bertholf R, Barkin RL, Webb F, Wilson G. Urine drug test interpretation: what do physicians know? J Opioid Manag. 2007;3:80-86.
Worker drug use and workplace policies and programs: results from the 1994 and 1997 National Household Survey on Drug Abuse. Substance Abuse and Mental Health Services Administration website. Available at: http://www.samhsa.gov/ .
Last reviewed January 2009 by ]]> Jill D. Landis, MD]]>
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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