Determinants of active and environmental exposure to tobacco smoke and upper reference value of urinary cotinine in not exposed individuals

The aims of this study were (1) to explore the behavioral and sociodemographic factors influencing urinary cotinine (COT-U) levels in active smokers and in environmental tobacco smoke (ETS)-exposed individuals, (2) to assess the specificity and sensitivity of the questionnaire for identifying active smokers and nonsmokers, and (3) to derive the upper reference value of COT-U in non-ETS exposed individuals. The COT-U levels of 495 adults (age range 18–69 years) who classified themselves as active smokers (29%) or as nonsmokers with (17%) or without (83%) ETS exposure were quantified by LC-MS-MS (quantification limit: 0.1µg/L, range of linearity: 0.1–4000µg/L). Median COT-U levels in these groups were 883, 1.38, and 0.39µg/L, respectively. Significant determinants of COT-U levels in active smokers were the number of cigarettes per day, type of smoking product, smoking environment, as well as time between the last cigarette and urine collection. Among ETS-exposed nonsmokers, significant determinants were living with smokers, being exposed to smoke at home, ETS exposure duration, as well as time between the last exposure and urine collection. When a 30-µg/L COT-U cut-off value was used to identify active daily smoking, the sensitivity and specificity of the questionnaire were 94% and 98%, respectively. For ETS exposure, the COT-U value of 1.78 (0.90 confidence interval 1.75–1.78) µg/L, corresponding to the 95th percentiles of the COT-U distribution in non-ETS-exposed participants, is proposed as upper reference value to identify environmental exposure.