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Measurement of Tobacco Smoke Exposure: Comparison of Toenail Nicotine Biomarkers and Self-Reports

¹ Moores UCSD Cancer Center, Department of Family and Preventive Medicine, University of California-San Diego, La Jolla, California; ² Department of Nutrition, Harvard School of Public Health; and ³ Channing Laboratory, Department of Medicine, Harvard Medical School and Brigham and Women's Hospital, Boston, Massachusetts

Requests for reprints: Wael K. Al-Delaimy, Moores UCSD Cancer Center, Department of Family and Preventive Medicine, University of California-San Diego, La Jolla, CA 92093. Phone: 858-822-6515; Fax: 858-822-2399. E-mail: wael{at}ucsd.edu

Background: Accurate measurement tools of exposure for use in large epidemiologic studies are lacking. Biomarkers of tobacco exposure provide additional advantages to self-reports and there is a need to further develop and validate them. The objective is to compare toenail nicotine levels, a novel biomarker of tobacco exposure, with self-reports of tobacco exposure from a large cohort study.

Methods: In this cross-sectional analysis, toenail samples were collected from 2,485 women participating in the Nurses' Health Study in 1982. Detailed self-reports of smoking habits and reported exposure to secondhand smoke (SHS) were collected from these women near the time of toenail collection. The toenail samples were analyzed by a high-performance liquid chromatography method for measuring nicotine.

Results: The 5 to 95 percentile range of toenail nicotine was from 0.06 to 4.06 ng/mg toenail and the median level was 0.21 ng/mg. There was a significant difference in toenail nicotine levels according to reported smoking status (the median level for nonsmokers with no SHS was 0.10 ng/mg, the median level for nonsmokers with SHS was 0.14 ng/mg, and the median level for active smokers was 1.77 ng/mg). However there was considerable overlap in nicotine levels according to reported smoking status. Toenail nicotine level was strongly associated with reported smoking level (Spearman r = 0.63), but there was no complete concordance, suggesting that the two methods are measuring different aspects of the same exposure.

Conclusion: Our findings show that toenail nicotine levels capture the overall burden of tobacco smoke exposure and provide additional information on exposure not captured by reported history. (Cancer Epidemiol Biomarkers Prev 2008;17(5):1255–61)