Optimal Serum Cotinine Levels for Distinguishing Cigarette Smokers and Nonsmokers Within Different Racial/Ethnic Groups in the United States Between 1999 and 2004

TLDR

Cotinine, a nicotine metabolite, is the standard biomarker for distinguishing smokers from nonsmokers in epidemiologic research. The study aims to identify updated serum cotinine cutpoints that reflect reduced secondhand smoke exposure and stricter indoor air regulations. Using NHANES 1999–2004 data from 3,078 smokers and 13,078 nonsmokers, the authors applied receiver‑operator‑characteristic curve analysis to determine optimal cutpoints. Optimal cutpoints were 3.08 ng/mL for adults and 2.99 ng/mL for adolescents, with substantial race/ethnicity variation (e.g., 5.92 ng/mL for non‑Hispanic blacks vs.

Abstract

Cotinine, a metabolite of nicotine, is widely used to distinguish smokers from nonsmokers in epidemiologic studies and smoking-cessation clinical trials. As the magnitude of secondhand smoke exposure declines because of proportionally fewer smokers and more clean-indoor-air regulations, the optimal cotinine cutpoint with which to distinguish smokers from nonsmokers is expected to change. The authors analyzed data on 3,078 smokers and 13,078 nonsmokers from the National Health and Nutrition Examination Survey for 1999–2004. Optimal serum cotinine concentrations for discriminating smokers from nonsmokers were determined using receiver operator characteristic curve analysis. Optimal cotinine cutpoints were 3.08 ng/mL (sensitivity = 96.3%, specificity = 97.4%) and 2.99 ng/mL (sensitivity = 86.5%, specificity = 93.1%) for adults and adolescents, respectively. Among adults, optimal cutpoints differed by race/ethnicity: They were 5.92 ng/mL, 4.85 ng/mL, and 0.84 ng/mL for non-Hispanic blacks, non-Hispanic whites, and Mexican Americans, respectively. Among adolescents, cutpoints were 2.77 ng/mL, 2.95 ng/mL, and 1.18 ng/mL for non-Hispanic blacks, non-Hispanic whites, and Mexican Americans, respectively. Use of the currently accepted cutpoint of 14 ng/mL overestimates the number of nonsmokers in comparison with the proposed new overall cutpoint of 3 ng/mL or the race/ethnicity-specific cutpoints of 1–6 ng/mL.