Determinants of Serum Cotinine as a Biomarker of Childhood Environmental Tobacco Smoke Exposure

Abstract

ISEE-678 Objective: Environmental tobacco smoke (ETS) is a major risk factor for diseases and disability among children. We evaluated the ability of a comprehensive set of factors to predict serum cotinine, a biomarker of recent ETS exposure. Materials and Methods: We included children from the Cincinnati Asthma Prevention Study, a randomized trial of air cleaners in the homes of 223 children with asthma living with 1 or more smokers. We collected data during home visits at baseline, 6 months, and 12 months: serum cotinine, an extensive parent interview of the child's ETS exposure, an air nicotine dosimeter cassette, housing volume and other objective measures of the home. To account for the within-subject correlation in this repeated measures design, we used linear mixed models with the natural log of serum cotinine as the outcome variable, adjusting for intervention status and study visit. The Akaike Information Criteria (AIC) was used as a measure of the relative predictive ability of competing models, with a decrease >10 indicating substantially better fit. Results: The nicotine dosimeter was the single best predictive variable, outperforming (decrease in AIC > 10) a model that combined parent report of maternal smoking, number of cigarettes, and hours spent in a room with smoking. Season, home volume, and ETS exposure outside the home (vehicles and others’ homes) predicted additional variability in serum cotinine. Even after accounting for these determinants of exposure, parent sociodemographic characteristics explained additional variability in serum cotinine (decrease in AIC > 20). Conclusions: We conclude that an objective measure of home ETS exposure, air nicotine dosimeters, performed better than parent report, but that serum cotinine is preferred in epidemiologic studies because it reflects a wider variety of ETS exposure determinants. When ETS is measured by parent report, adjustment for sociodemographic characteristics may result in underestimation of the effect of ETS.