Effect of Sample Storage Conditions on Measurements of Salivary Cotinine Levels

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.

Effect of Smoking Exposure on Nonsurgical Periodontal Therapy: 1-Year Follow-up

“…Considering that the degree of exposure to smoking is important, information on the number of cigarettes consumed per day was recorded in the questionnaire, yet there was a discrepancy between the reported number and the cotinine levels. This bias was already observed in people with systemic chronic diseases and during pregnancy (Pell et al 2008;Dietz et al 2011;Leite et al 2020). Different phenomena explain the underreport of tobacco use, such as recall bias, response bias to the undesirability of smoking, and the Hawthorne effect since people change behaviors when under surveillance (Williams et al 2020).…”

“…For assessing current smoking, an exhaled carbon monoxide (CO) reading in parts per million was taken at every visit (Micro Smokerlyzer; Bedfont Sci Ltd), followed by a salivary test for cotinine (Salimetrics). More information is available elsewhere (Leite et al 2020).…”