Smoking is the main risk factor for lung cancer, accounting for nearly 85% of cases in men and 50% of cases in women worldwide (1,2). Smoking exposure is usually assessed through questionnaires (e.g. cigarettes per day (CPD) and duration of smoking); measures that have several limitations (3). Circulating levels of cotinine, the nicotine metabolite, provide an accurate measure of recent tobacco smoke exposure and are able to account to some degree for individual differences in smoking practices, such as depth of inhalation and how completely each cigarette is smoked (4,5). Cotinine has a half-life of approximate 17 hours and reflects active and second-hand smoking and smoking intensity over the last 1-2 days (4,5).
