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APA: Drug Test Results Often Flawed
By Kristina Fiore, Staff Writer, MedPage Today
Published: May 23, 2010
Reviewed by Robert Jasmer, MD; Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, RN, BC-ADM, CDE, Nurse Planner

NEW ORLEANS -- That poppy seeds can lead to false-positive results on tests for opioid abuse is not just an urban legend, researchers said here.

Amounts as small as a teaspoon -- at least the amount on a poppy seed bagel -- can trigger a positive finding, and can last for two to three days after consumption, according to Dwight Smith, MD, of the VA medical center in Black Hills, S.D., and colleagues.

The example is one of many suggesting that drug-abuse tests often give inaccurate results, according Smith's presentation here at the American Psychiatric Association's annual meeting.

Another example is that most standard drug tests don't screen for the opioid drug oxycodone, as well as a handful of other opioids including methadone and fentanyl, noted Smith, who conducted the research while he was at Boston Medical Center. Physicians must specifically order these assays.

"There are gaps in our understanding of the science behind drug tests, and how that leads to our interpretation of testing results," said Smith. That's one of the reasons he and his colleagues conducted a review of the literature on drug tests, their scientific background, and potential clinical concerns.

The latter are particularly important because drug screens are so common, Smith said. Last year, about 150 million drug tests were conducted in the United States.

"We drug test everyone in the states nowadays -- our students, our athletes," he said. "It's a condition for employment in many federal and private agencies."

Still, many physicians may not be aware that ordering a general "drug test" won't cover all their bases, or that half of patients who are abusing substances will be missed.

One study in the review found 88% of physicians were unaware of the need to request the specific oxycodone assay, and half did not know about the false-positives associated with poppy seeds.

Opioid tests screen for morphine and codeine, which are two of the most common metabolites of many -- but not all -- opioids. They're not metabolites of oxycodone, methadone, fentanyl, tramadol (Ultram), and buprenorphine (Subutex, Suboxone), Smith said.

"You need to order the specific assays in order to accurately interpret those," he added.

Similarly, only certain metabolites of benzodiazepines are detected on most assays. That means diazepam, nordiazepam, and oxazepam (Serax) will be detected, but alprazolam (Xanax), lorazepam (Ativan), and clonazepam (Klonopin) aren't frequently screened.

Part of the problem is that there are no federal guidelines for minimum negative threshold levels for a positive test, Smith said. Plus, each laboratory has its own guidelines and procedures for dealing with test sensitivity and specificity.

In their review, the researchers found that drug tests generally have a sensitivity of 90% to 95%, and a specificity of 85% to 90%. These numbers are a "pretty good basis" for making clinical decisions, Smith said, but that means "one in 20 [tested patients] are going to have inaccurate results, and those are more likely to be false positive than false negative."

By comparison, confirmatory tests such as gas-chromatography mass-spectrometry have a sensitivity of 99% and a similar specificity, but they are more expensive.

Physicians "trust in science, and we believe [sensitivity and specificity] are going to be higher than that when they're not," he said. "We really need to get tests confirmed."

Many substances aside from poppy seeds cause these false-positives. Cold medications can give a positive read on amphetamines, as can bupropion (Wellbutrin) and tricyclic antidepressants.

Sertraline (Zoloft) and oxaprozin (Daypro) can alert physicians to a benzodiazepine problem when there is none.

The HIV medication efavirenz (Sustiva) can come up as a positive for marijuana use, and dextromethorphan, rifampin, and quinolones could show as an opioid problem.

"If a patient does test positive, you need to take a careful medical history," Smith said.

Smith also did some myth-busting, finding that there's no possibility of a false positive resulting from passive inhalation of marijuana or cocaine -- unless they are exposed to an excessively concentrated amount of smoke.

"If a patient comes in and blames it on any of these scenarios, you can say, 'Unless you were in the van with Cheech and Chong, that's not what happened,'" Smith said.

As far as false-negatives go, Smith said physicians should be wary of the methods for diluting samples used in drug tests -- an issue he calls "the elephant in the room."

On average, such strategies appear to work 50% of the time. These include bleaching urine or adding the household cleaner Drano or the eye lubricant Visine to it.

Others have gone to great lengths to design battery-powered devices that keep urine warm, and offer a prosthetic device "in three or four skin tones" for the most cunning of drug test cheaters, Smith said.

A fail-safe would be to screen the urine for its standard specific gravity of greater than 1.003, or standard creatinine above 20 mg/dL.

Yet no studies have been done to show exactly how prevalent drug test cheating is, Smith said, adding that the area urgently needs research.

His advice to physicians who want to know the quality and the specifics of the drug test reports they receive: "Become friends with the toxicologist in charge of the lab. It's particularly helpful if the results of the test are unexpected."

The review was based on studies found via a PubMed search between Jan. 1, 1980 and Sept. 1, 2009.

Ronald Bugaoan, MD, medical director of High Point Treatment Center in Brockton, Mass., who assisted in the study, said urine tests do indeed have the longest window of detection for most substances.

However, gas-chromatography mass-spectrometry is the "gold standard" for drug testing, and added that patients enrolled in the Massachusetts health plan can get tests using it for only $12 apiece

The researchers reported no conflicts of interest.

Primary source: American Psychiatric Association
Source reference: Smith D, et al "An update on testing for drugs of abuse: Scientific background and practical clinical concerns" APA 2010; Abstract NR7-05.

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