Interference of tobacco smoke with immunochromatography assay for urinary drug detection.

Background: This study aimed to evaluate the interference of tobacco smoke on immunochromatography assay of urinary drug detection.

Methods: Our study included 256 voluntary subjects (143 passive smokers and 113 current smokers). Cotinine was measured by immunoenzymatic method and thiocyanates (SCN(-)) by selective electrode. Urinary drug was detected by immunochromatography assay. A positive result is completed by an analytical method with an immunometric assay.

Results: False positive results for benzodiazepines are significantly more frequent in smokers compared with passive smokers (90.2% Vs 22.4%; χ(2) = 116.62, p < 10(-3)). For smokers, the number of cigarettes was significantly higher in subjects with falsely positive results for benzodiazepines compared with subjects with negative results (32 ± 11 Vs 20 ± 10; p = 0.04). Between these two groups, we established a significant difference for urinary cotinine (345 ± 211 Vs 117 ± 54 μg/μmol; p < 10(-3)) and for plasma SCN(-) (101.6 ± 3.4 Vs 98.8 ± 2.1 μmol/L; p = 10(-3)). Urinary cotinine and consumption duration present the highest values of areas under curves (AUC) of the receiver-operating-characteristic (ROC) curves. The cut-off of 167.6 μg/μmol and 10.5 years were found as predictive factors of false positive results.

Conclusion: Tobacco smoke interferes with immunochromatography assay of urinary drug detection; therefore, all subjects must be questioned about their smoking status to avoid such false results during results interpretation.