The validation of self‐reported smoking status by analysing cotinine levels in stimulated and unstimulated saliva, serum and urine

OBJECTIVES: Cotinine, a nicotine metabolite, can be used to measure exposure to tobacco smoke. The aim of this study was to compare cotinine levels in different biological fluids collected from both smokers and non-smokers and to relate the findings to self-reported smoking status. Data were also collected concerning the acceptability of the differing methods of sample collection. MATERIAL AND METHOD: Patients recruited to the study were asked to provide samples of urine, blood and saliva (both stimulated and unstimulated). Data collected from patients by questionnaire included information on smoking behaviour such as daily number of cigarettes and environmental exposure to smoke. After the sample collection, patients were asked to rate the acceptability of each sampling method. Samples were analysed using enzyme immunoassay (EIA) kits. RESULTS: In total, 80 patients participated, with 49 being smokers and 31 being non-smokers. There was clear differentiation between smokers and non-smokers (P < 0.001) for all the different samples in terms of cotinine. A significant relationship was seen between cotinine and daily number of cigarettes for both salivas and urine (all P < 0.001) but not for serum. Participants found serum and urine collection methodologies 'very acceptable' (67 and 66%, respectively) whereas 9% found collection of stimulated saliva 'not at all acceptable'. CONCLUSION: Cotinine, whatever the collection method and analysed by EIA kits, shows good differentiation between smokers and non-smokers. Salivary samples have the advantage of being non-invasive, although collection methodology is important, as cotinine levels may vary.