FALSE POSITIVES ARE COMMON IN DRUG TESTS ON NEW MOMS SCREENING: UP TO 70 PERCENT OF INITIAL CHECKS CAN BE WRONG.

Byline: Troy Anderson

Staff Writer

Hospitals' initial urine- screening drug tests on pregnant women can produce a high rate of false positives -- particularly for methamphetamine and opiates -- because they are technically complex and interpretation of the results can be difficult, some experts say.

Tests for methamphetamine are wrong an average of 26 percent -- and possibly up to 70 percent -- of the time, according to studies by the University of Kansas Medical Center, U.S. Substance Abuse and Mental Health Services Administration and the American Association for Clinical Chemistry.

And even the gold standard of maternal drug testing -- meconium, a baby's first stool that is analyzed to assess a mother's drug usage over the past four or five months -- can produce false positives for methamphetamine up to 70 percent of the time, said Dr. Barry Lester, a national expert on drug-exposed babies and a professor of pediatrics and psychiatry at Brown University in Providence, R.I.

False positives can be triggered by everything from cold medicines and diet pills to poppy seeds, according to a January study by the University of Kansas published in Mayo Clinic Proceedings.

The study found cold remedy compounds, herbal medications and doctor-prescribed medicines for anxiety or depression often produce false positives for methamphetamines.

On average, the study found initial urine screens for methamphetamines produced false positives 26 percent of the time. For opiates, the percentage rose to 29 percent. Less than 8 percent of tests for cocaine and marijuana resulted in false positives.

"There is a relatively good chance that there will be a false positive for those particular drugs (methamphetamine and opiates)," said Dr. Donald Frederick, chairman of the toxicology division at the American Association of Chemistry in Washington, D.C.

"I always recommend they go to confirmatory or forensic testing if they are going to use any clinical immunoassays for legal purposes."

Hospital doctors have the discretion whether to request an initial urine screen and usually do so only if the mother exhibits signs of drug use, the baby is born premature or underweight, or other reasons occur.

If a test is positive, many hospitals perform confirmatory tests to ensure the results are accurate -- but some don't.

The U.S. Substance Abuse and Mental Health Services Administration said the federal government has required confirmatory tests for its employees since 1988 to help eliminate false positives. Confirmatory tests usually involve gas chromatography and mass spectrometry.

But James Lott, executive vice president of the Hospital Association of Southern California, said it's not the hospital's responsibility to conduct confirmatory drug tests.

"It's not the hospital's burden to do a confirmatory test," Lott said. "It's up to the agency that investigates child abuse whether a confirmatory test needs to be done.

"The hospital can choose to do it if it wants to, but it's not obligated to do it."

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