MISCLASSIFICATION OF SMOKING STATUS IN THE CARDIA STUDY - A COMPARISON OF SELF-REPORT WITH SERUM COTININE LEVELS

Background. Although widely used in epidemiological studies, self-repo rt has been shown to underestimate the prevalence of cigarette smoking in some populations. Methods. In the CARDIA study, self-report of cig arette smoking was validated against a biochemical marker of nicotine uptake, serum cotinine. Results. The prevalence of smoking was slightl y lower when defined by self-report (30.9%) than when defined by cotin ine levels equal to or greater than 14 ng/mL (32.2%, P < .05). The mis classification rate (proportion of reported nonsmokers with cotinine l evels of at least 14 ng/mL) was 4.2% and was significantly higher amon g subjects who were Black, had a high school education or less, or wer e reported former smokers. Possible reasons for misclassification incl ude reporting error, environmental tobacco smoke, and an inappropriate cutoff point for delineation of smoking status. Using self-report as the gold standard, the cotinine cutoff points that maximized sensitivi ty and specificity were 14, 9, and 15 ng/mL for all, White, and Black subjects, respectively. The misclassification rate remained significan tly higher in Black than in White subjects using these race-specific c riteria. Conclusion. Misclassification of cigarette smoking by self-re port was low in these young adults; however, within certain race/educa tion groups, self-report may underestimate smoking prevalence by up to 4%.