NEW ORLEANS – Some of the most important drugs of abuse, misuse, and diversion remain undetected by common immunoassay drug screens, according to Dr. Dwight Zach Smith.
Moreover, widely used drug screens produce false-positive results in as many as 1 in 10 cases.
“We trust in science. We believe [accuracy] is going to be higher than that, when it's not. We need to have these tests confirmed,” Dr. Smith, a psychiatrist with the Veterans Affairs Black Hills (S.D.) Health Care System, said at the meeting.
Dr. Smith and his associates reviewed nearly 30 years of peer-reviewed studies concerning the coverage, accuracy, and specific nuances of commercially available drug-screening immunoassays and found that, although they have improved, they are “not so good.”
Drug testing, he said, “is simply a fact of life in America in the 21st century,” with one drug-screening test performed for every two Americans in 2009.
“We have drug tests for our students, for our athletes, [and] as a condition for employment for many federal and private agencies,” he noted.
Considering how prevalent they are, however, “unfortunately there remains a significant gap in our knowledge and our scientific understanding of drug tests [pertaining to] clinical practice,” Dr. Smith said.
For example, a 2007 study included in the review found that 88% of physicians did not realize that oxycodone is not detected in most opiate assays.
They also might be surprised to learn that methadone, fentanyl, tramadol, hydromorphone, and buprenorphine also go largely undetected in opiate immunoassays, unless a physician specifically requests them, he said during a session on issues within addiction psychiatry.
Benzodiazepine drug screens report on use of diazepam, nordazepam, and oxazepam, but “surprisingly to me,” not some of the most commonly misused drugs within the class, including clonazepam, alprazolam, and lorazepam, Dr. Smith said.
Unlike other drug classes, benzodiazepine screens are regulated by no federal guidelines establishing minimal thresholds for defining a positive test result. “Each lab sets its own minimal thresholds, sets of guidelines, and procedures … with differing specificities and sensitivities,” Dr. Smith pointed out.
Dr. Smith advised physicians requesting drug screens to be very specific about what they want and to “become friends with the toxicologist in charge of the lab” to discuss laboratory standards and unexpected test results.
Ordering a confirmatory test using gas chromatography/mass spectrometry also is a useful step in the face of unexpected results, but cost is a barrier for some. A standard immunoassay might cost $12, compared with almost $120 for the much more accurate confirmatory test (99% sensitivity, 99% specificity), he said. Another problem with drug screening arises when a careful medical history is not taken before the ordering of a drug screen, he said.
False-positive results might arise if a patient is taking sympathomimetics such as Vicks nasal inhaler, tricyclic antidepressants, bupropion, selegiline, ranitidine (false-positive amphetamine results); sertraline or oxaprozin (false-positive benzodiazepine results); efavirenz or hemp-containing foods (cannabis); or poppy seeds, dextromethorphan, rifampin, or quinolones (false-positive opioid results).
With regard to poppy seeds, 1 teaspoon or more within 2-3 days of a test could alter results.
False-positive test results are a relatively common phenomenon with immunoassays used for the majority of drug-screening tests in the United States, with a mean specificity of 85%-90%, his research found.
“I look at those numbers, and I can't help but think 1 in 10 … are going to be inaccurate results,” he said.
Sensitivities are better, at about 90%-95%, but that range does not account for myriad ways drug users thwart the test results: by drinking a gallon of water, diluting urine with bleach or drain cleaner, or using someone else's urine to fill a commercially available product such as the “Real Whizzinator,” a device that contains a prosthetic penis with synthetic urine for men who seek to pass drug tests.
He estimated that about half of cheaters get away with their ruse, since many laboratories do not check samples for urine-specific gravity, creatinine, pH, or exogenous substances that might give them away.
Dr. Smith reported he had no relevant financial conflicts.
Widely used drug screens produce false-positive results in as many as 1 in 10 cases; the results need to be confirmed.
Source DR. SMITH