Observations on the number of saliva cotinine positives over a nine-year period

Passive smoking (usually seen in people who live with smokers) also has an impact on health.3·4 When nicotine from tobacco smoke is taken into the lungs and enters the bloodstream, it is metabolised in the liver and converted to cotinine by enzymes such as cytochrome P450 2A6, then eventually excreted in the urine as trans-3'hydroxycotinine.5-6 Cotinine diffuses easily from the blood into saliva, and salivary and blood levels have been shown to correlate.7-8 Cotinine in saliva has a longer half-life than nicotine (greater than 10 hours), and is a specific and sensitive marker for determining exposure to tobacco and nicotine both in smokers and passive smokers.' Previous cut-off levels were 10 ngfaiL: anything greater was considered as positive and consistent with smoking, and anything less was considered negative.10 In more recent years, this cut-off has been changed to 13 ng/mL and now includes an equivocal range of 7-13 ng'mL, to try to discriminate between active smokers, passive smokers and non-smokers.11-13 Up to March 2011, Quest Diagnostics provided services for a number of insurance companies to test potential life insurance clients for smoking by measuring salivary cotinine levels as part of the application criteria.