Cotinine is a stable metabolite of nicotine, and is the most widely used biomarker to measure tobacco use and exposure, i.e. both active and passive smoking. Serum cotinine has a half-life of 15 to 40 h and reflects tobacco exposure during the prior 3 to 5 days. The half-life of cotinine is longer than that of nicotine. Thus, the cotinine concentration is therefore rather stable throughout the day.
Assessment of smoking status and tobacco exposure.
Matrix: Serum, EDTA plasma, saliva and urine.
Volume: Minimum volume is 60 µL, but 200 µL is optimal and allows reanalysis.
Preparation and stability: Cotinine is stable.
The information below applies to measurement in serum or plasma.
Non-smokers < ~5 nmol/L; passive smokers 5 – 85 nmol/L; smokers > 85nmol/L; heavy smokers (>25 cigarettes/day) > 1700 nmol/L.
To convert from SI unit (nmol/L) to conventional unit (µg/L), multiply the SI value by the conversion factor = 0.1762.
Nicotine patches and snuff give very high plasma cotinine levels.
Serum cotinine cut-off distinguishing smoker from non-smoker varies between studies from 57 to 114 nmol/l, and 85 nmol/L is the value suggested in most studies. But as smoking prevalence declines, so does exposure to environmental tobacco smoke, and lower cut-off values seem to be obtained (2).
Intraclass correlation coefficient (ICC): 0.92 (3).
1. Midttun, O., Hustad, S., and Ueland, P.M. (2009). Quantitative profiling of biomarkers related to B-vitamin status, tryptophan metabolism and inflammation in human plasma by liquid chromatography/tandem mass spectrometry. Rapid Commun Mass Sp 23, 1371-79.
2. Kim, S. (2016). Overview of cotinine cutoff values for smoking status classification. Int J Environ Res Public Health 12.
3. Midttun, O., Townsend, M.K., Nygård, O., Tworoger, S.S., Brennan, P., Johansson, M., and Ueland, P.M. (2014). Most blood biomarkers related to vitamin status, one-carbon metabolism, and the kynurenine pathway show adequate preanalytical stability and within-person reproducibility to allow assessment of exposure or nutritional status in healthy women and cardiovascular patients. J Nutr 144, 784-790.