Abstract
Information on smoking exposure obtained with self-reports may be inaccurate. Cotinine has a large half-life and its salivary levels correlate well with plasmatic levels. The influence of storage conditions on the validity and precision of salivary cotinine assessments has rarely been evaluated. Here, smokers donated saliva samples, which were sent for immediate analysis, mail posting, storage at 4 °C for 30 or 90 days, or storage at −20 °C for 30 or 90 days. Cotinine levels were determined using enzyme-linked immune-sorbent assay. Agreement of cotinine level measurements was assessed using Bland-Altman analyses. Average age (years), duration of smoking (years) and number of cigarettes smoked (/day) were 55.4 (±SD 9.4), 35.1 (±SD 11.3), and 15.3 (±SD 7.6). The mean immediate cotinine level was 457 ng/mL (range 11.3 to 1318 ng/mL). Mean cotinine levels in samples analyzed after delay ranged between 433 ng/mL (−20 °C 30 days) and 468 ng/mL (4 °C 30 days). A dose-response gradient was observed in the relationship between salivary cotinine level and self-reported smoking status. A good agreement between cotinine levels for all storage conditions compared with immediate analysis was observed, with average differences ranging from −11 to 24 ng/mL. Cotinine levels remained stable regardless of the tested condition. The stability of salivary cotinine may enable samples to be obtained in difficult-to-reach areas, reduce study costs, and improve the validity of the information on exposure to smoking.
Highlights
The assessment of exposure to tobacco smoking and nicotine may be required in different settings, such as sports, as well as for clinical and research purposes
The mean cotinine levels ranged between 433 ng/mL and 468 ng/mL
We compared the recordings of cotinine levels observed in aliquots from the same saliva sample stored under different conditions, and found that cotinine levels remained stable regardless of the tested condition
Summary
The assessment of exposure to tobacco smoking and nicotine may be required in different settings, such as sports, as well as for clinical and research purposes. Nicotine may have an ergogenic effect and benefit the physical performance of athletes [1]. Assessment of exposure to tobacco and nicotine may be necessary for legal reasons and for monitoring purposes in smoking cessation programs [3,4,5]. Valid and reliable information on smoking and nicotine is needed to evaluate the level of exposure to tobacco or for the purpose of controlling for confounding in statistical analyses of other exposures that might be related to smoking.
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