DES MOINES, Iowa (AP) -- A federal judge has upheld a lower court's ruling that drug-detecting sweat patches are a reliable method to determine whether an offender has violated conditions of probation.

In its ruling Wednesday, the St. Louis-based 8th U.S. Circuit Court of Appeals said it was the first time it had expressed a view on the general reliability of the drug testing method.

The court upheld the ruling of a federal district court judge in a case against Mark Lou Meyer, of Cedar Rapids. Records showed he had eight positive sweat patch results, "and the reasons he advanced to support his argument that the results were false positives were wholly unpersuasive," the court wrote in a summary of the case.

Meyer was indicted on Jan. 22, 2004, for being an unlawful drug user in possession of a firearm. He pleaded guilty and was sentenced on Sept. 2, 2004, to a term of three years' probation. The conditions prohibited him from possessing or using unlawful drugs, and from leaving Iowa's northern district without permission from the court or a probation officer.

Meyer had to wear sweat patches and undergo urine tests during the probation. Court records said that eight of 16 patches submitted from November 2005 to June 2006 tested positive for cocaine and a cocaine metabolite. None of the urine samples Meyer submitted from March 2006 to June 2006 indicated that he had been using unlawful drugs.

U.S. attorneys filed a motion to revoke Meyer's probation on May 31, 2006, because of the positive sweat patch results, but Meyer denied taking illegal drugs.

During three district court evidentiary hearings, a biochemist testified that the FDA-approved patches are scientifically reliable but admitted that some academic papers concluded they could become contaminated without the wearer having used drugs. The expert also testified that Meyer's negative urine and positive sweat patch results could be reconciled because there was an insufficient amount of the drug to trigger a positive urine results, but enough to show a modest amount of cocaine usage on the patch.

Meyer argued that the company he worked for transported high-end cars, and that he could have been contaminated while hauling the cars.

"There would have been a chance, and every chance, for me to come in contact with contamination from somebody that had done drugs in their cars, touched a steering wheel, touched the gearshift, touched the door handle," he testified. "Somebody could have been smoking in there."

Meyer's probation officer also testified that he left the state without permission.

The district court revoked Meyer's probation and sentenced him to six months in prison, followed by two years supervised release.

In its ruling Wednesday, the 8th Circuit said it would join other courts that have previously determined that sweat patch results are a "generally reliable method of determining whether an offender has violated a condition of his or her probation."

Because there may be instances where offenders offer compelling reasons to believe the positive test results are erroneous, the district court should make a case-by-case determination as to the tests' reliability, the court wrote.

However in Meyer's case, it said "Meyer's effort to support an environmental explanation for his positive sweat patches is wholly unpersuasive." It backed the expert testimony on how the urine results could be reconciled, and the court said a negative hair sample was determined not to be as reliable of an indicator of drug usage.

Meyer's attorney Michael Mollman said while they respect the decision of the 8th Circuit, "my client may decide to see if the supreme court will take the case."