Cotinine

cot

What is cotinine?

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.

Indication(s)

Assessment of smoking status and tobacco exposure.

Specimen, collection and processing

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.

Transportation

Frozen, on dry ice. (for general instruction on transportation, click here)

Interpretation and cut-off values

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).

Literature

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.

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