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March 25, 1988

Use of Urinary Cotinine to Estimate Exposure to Tobacco Smoke

JAMA. 1988;259(12):1808. doi:10.1001/jama.1988.03720120016013

To the Editor.  —Sepkovic and colleagues1 report that the half-life of cotinine in nonsmokers is 2.7 times that in smokers and that this difference "precludes a direct extrapolation to 'cigarette equivalents of smoke uptake' from a single measurement of urinary cotinine."1,2 This conclusion seems unjustified since, even if there is a difference, once the magnitude of the difference has been established this can be taken into account when estimating the relative exposures of smokers and nonsmokers to tobacco smoke. In addition, there appears to be an error such that the difference is less than 2.7-fold. While the report by Sepkovic et al1 reports a mean half-life of 18.5 hours (n = 10) for smokers and 49.7 hours for nonsmokers (n = 4), yielding a ratio of 2.7, the data presented in the figure that accompanies the report show that the half-life is about 27 hours for the nonsmokers rather