False Positives from Personal Radical Shield?

Q I have never smoked in my life, yet a recent urine test showed that I’m a smoker! Could the use of Personal Radical Shield have anything to do with this bogus result?

CHERYL, Houston

A Virtually all lab tests are subject to a certain percentage of false positives. In tests for tobacco, certain drugs, and certain dietary substances, such as isoniazid, high doses of niacin or other substances with a similar molecular structure may interfere with the assay and cause false positives.1 Personal Radical Shield contains niacin (also known as nicotinic acid because it’s an oxidation product of nicotine), a B-vitamin that serves many purposes in the body. The way to handle your situation is to insist on a test that measures carbon monoxide levels in expired air or in the blood, or on any other test that does not rely on the measurement of nicotine or its metabolites in the urine.


  • SRNT Subcommittee on Biochemical Verification. Biochemical verification of tobacco use and cessation. Nicotine Tob Res 2002 May;4(2):149-59.

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