Employer Drug Tests May Not Detect Prescription Drugs

By Frank Klimko Sep 1, 2008

Not all drug-screening methods used by employers are able to detect some of the prescription drugs that are being abused​—such as opiates like Vicodin—a researcher who studies workplace drug testing told SHRM Online.

Workplace drug testing has gotten significantly more accurate in recent years, but some tests do not pick up trace amounts of certain drugs, John Mitchell, co-director of the Center for Forensic Sciences at RTI International in Research Triangle Park, N.C., said during the Substance Abuse and Mental Health Services Administration’s (SAMHSA) Drug Testing Advisory Board (DTAB) meeting on Aug. 20, 2008, in Rockville, Md.

Employers need to know what substance to test for, or what drugs a specific test will detect, he said. For example, one of the drug panels commonly used for workplace testing detects opiates only 20 percent of the time that a competing drug panel does. Some tests lack sensitivity at detecting prescription drugs because when the tests were developed, the focus was on illicit drugs and not on drugs obtained with a prescription, Mitchell said.

The test panels established decades ago by the National Institute on Drug Abuse (NIDA) list drugs under five groups, since called the “NIDA-5.” The test panels are useful, but do not always account for current drug usage patterns, excluding semi-synthetic opioids such as oxycodone, oxymorphone, hydrocodone and hydromorphone, Mitchell said.

In general, the greater the number of drugs targeted, the higher the cost of a test, which means that many employers only target the NIDA 5, which are:

Cannabinoids (marijuana and hashish, tests for metabolite THCCOOH).

Cocaine (cocaine, benzoylecognine and cocaethylene, tests for cocaine metabolite).

Amphetamines (amphetamine and methamphetamine).

Opiates (heroin, opium, codeine, morphine and 6-MAM).

Phencyclidine (PCP).

Some tests are better than others, and HR staff should talk with their contracted testing laboratories to make clear the kinds of drugs to screen for, Mitchell said.

There are other ways to increase the accuracy of the drug tests. HR staffers should shy away from single-phase presumptive tests that can generate a high proportion of false negative and false positive results, Mitchell said.

The majority of tests administered in pre-hire and even most probate scenarios are of the immediate, less accurate “at home” variety. For example, an initial drug screen could detect traces of morphine, but it would take a second, more detailed, analysis to determine whether the positive result was actually morphine or an opiate, which can produce structurally similar test results to morphine, Mitchell said.

With a single drug screening that tests positive, an employer probably will not know what caused the positive result, Mitchell said. “You may be throwing away a perfectly good employee with using just one test.”

A more accurate regime includes a first-stage presumptive test and a second-stage confirmatory test that verifies whether drugs were found. After a suspected positive sample is detected during screening, the sample is flagged and tested using the confirmation test, Mitchell noted.

The confirmation test in most laboratories (and all SAMHSA certified labs) is performed using mass spectrometry, and is extremely precise. Samples testing positive during both screening and confirmation tests are reported as positive. For workplace drug testing, a positive result is generally not confirmed without a review by a “medical review officer” who will normally interview the subject of the drug test.

Frank Klimko is a Washington, D.C.-area writer with experience covering federal regulatory agencies.


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