Table 1.

Cutpoints and time after smoking cessation to reach cutpoint to distinguish smokers and nonsmokers (based on average precessation levels, cigarette smoking, and U.S. population data)

	Detects		Cutpoint	Average half-life	Approximate time to cutpoint
Free cotinine plasma, saliva, and urinea	Exposure to nicotine from all sources (e.g., combustible, noncombustible, and NRT)		3–10 ng/ml 30–50 ng/ml	16 h	80–100 h
CO (exhaled air)	Consumption of combustible tobacco and nontobacco (e.g., marijuana) products		5–6 ppmb	2–8 h depends on physical activity level	12–24 h
Minor tobacco alkaloids (urine)	Exposure to tobacco-derived nicotine products (e.g., cigarettes, cigars, and smokeless)	Anabasine Anatabine Nicotelline	2 ng/ml 2 ng/ml ?	16 h 10 h 2–3 h	80 h 50 h 10 h
NNAL (urine)	Exposure to cured tobacco (e.g., cigarrettes, cigars, and smokeless)		10–40 pg/ml	10–40 days	2–3 months

NNAL = 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol; NRT = nicotine replacement therapy.

^aUrine provides the highest concentration of cotinine and, thus, has the greatest sensitivity but also more between-sample variability. Plasma and saliva provide similar results, with lower concentrations, but with more between-sample stability.

^bAt one end of the continuum (e.g., in a country with high smoking prevalence and relatively weak legislation requiring smoke-free public places in industrial cities with high levels of air pollution), we recommend that the previous cutpoint of <10 ppm to validate a self-report of smoking abstinence for at least 24 h may still be appropriate. At the other end of the continuum (e.g., in places with strong smoke-free legislation, low smoking prevalence and relatively low levels of air pollution), we recommend that a cutpoint as low as <5 ppm will be more appropriate. Investigators should select the appropriate cutpoint (from 4 to 10 ppm) for their research and clinical purposes bearing these known factors (as well as brand/model of monitor) in mind.²⁵