NEW YORK (Reuters Health) - School-based drug testing has been proposed as a way to fight teen drug abuse, but a study published Monday suggests that many test results could be easily misinterpreted.

In particular, researchers found, standard drug screening tests would do little to spot teenagers who are abusing the painkiller oxycodone -- an increasingly popular drug of choice among teens.

The study, published in the April issue of Pediatrics, focused on a random drug testing program conducted as part of a teen substance abuse program at Children's Hospital Boston.

The drug testing involved rigorous procedures; to give a urine sample, for example, the teenagers had to show ID, empty their pockets and take nothing into the bathroom with them. The bathroom had no running water, so the teens could not dilute the urine sample to alter the test results; even the toilet water was dyed blue to make it unusable.

The drug testing itself involved two steps: the first was a screening test that looked for multiple drugs of abuse; then, if those results were positive, more-sophisticated testing was done to confirm the results.

Because the initial screening tests do not reliably detect oxycodone or other so-called opioids, samples from teens with a history of opioid abuse underwent additional testing regardless of what the screening results were. Finally, all of the samples were tested for signs of dilution -- which the teens could have accomplished by drinking large amounts of water before their test.

Had all of these control measures not been taken, there would have been ample opportunity for errors in the test results, the study found.

Of 710 drug tests, 40 that initially screened "negative" for drug use were found to be too dilute to yield reliable results. What's more, of 43 tests that confirmed oxycodone abuse, only 16 had tested positive during the first screening test.

The problem is that mass screenings at schools would be unlikely to include the extensive testing and rigorous procedures used in this teen drug abuse program, according to the study authors, led by Dr. Sharon Levy.

An expansive drug-test panel, beyond the routine screening tests, would be "prohibitively expensive," Levy told Reuters Health. And using only the screening tests would mean, for starters, that many cases of oxycodone abuse would go undetected.

There's also the chance of teens testing positive for drug abuse on the initial screen when they're not abusing drugs. Certain cross-reacting chemicals in foods and medications can lead to false-positive results; for example, certain cold medicines, and even high doses of caffeine, can cause a positive result for amphetamines.

In this study, most of the tests that were positive for amphetamines resulted from legitimate use of prescription or over-the-counter medications.

"Misinterpretation of test results, in either direction, can have devastating consequences," Levy said -- whether than means missing teens who are in trouble, or falsely accusing those without a drug problem.

Drug testing is a complex procedure, she said, and one best left to those with expertise.

The White House's Office of National Drug Control Policy is among those who've come out in favor of school-based drug screening. But, Levy said, "a lot of questions remain" about how effective such testing could be. A better option, she suggested, might be to be use standard screening questionnaires to spot kids at risk of drug abuse.