Interference of Gemfibrozil with Roche TesTcup

Journal of Analytical Toxicology, Vol. 23, September 1999 I ILetter to the Editor Interference of Gemfibrozil with Roche TesTcup To the Editor: As part of a workplace drug-testing policy, a coal-mining company implemented random on-site preliminary urine testing using the OnTrak TesTcup (Roche Diagnostic Systems, Inc.). Presumptive positives were sent to our laboratory for confirmation. A potentially embarrassing situation arose when the mining manager underwent a random test and produced a positive reaction to cannabinoids. He denied using any illicit drugs and claimed to be taking Gemfibrozil (Lopid) for treatment of hypertriglyceridemia. Upon receipt at the laboratory, the TesTcup still showed a positive reaction to cannabinoids. The urine specimen was analyzed for cannabinoids using EMITTM (Behring Diagnostics) at the 50-1Jg/L cutoff and was found to be negative. The urine specimen was then analyzed for the presence of carboxy-THC using pentafluoropropyl derivatization and gas chromatography-mass spectrometry (GC-MS). No carboxy-THCwas detected. The same sample was tested for cannabinoids using the Syva RapidTest (Behring Diagnostics). The test was negative. Gemfibrozil was added to drug-free urine and subjected to the same tests. No false positives were obtained. Urine was later obtained from a healthy subject taking only Gemfibrozil medication. The urine was subjected to the TesTcup (positive), EMIT (negative), and Syva RapidTest (negative). The urine was subjected to a comprehensive drug analysis including EMIT, high-performance thin-layer chromatography, and GC-MS. No drugs other than gemfibrozil were detected. Gemfibrozil is metabolized to hydroxymethyl and carboxyl products. It i~ suggested that one of these metabolites is responsible for the false-positive result of the Roche TesTcuptest for cannabinoids in urine. J.H. Lewis ToxicologyUnit Pacific Laboratory Medicine Services North Ryde NSW 2113 Australia :]84 Reproduction (photocopying) of editorial content of this journal is prohibited without publisher's permission.  (...truncated)