Effect of Sample Storage Conditions on Measurements of Salivary Cotinine Levels

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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.
Original languageEnglish
Article number365
JournalMetabolites
Volume10
Issue9
Number of pages10
ISSN2218-1989
DOIs
Publication statusPublished - 2020

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