Serum cotinine predicts bronchial obstruction regardless of self-reported smoking history

Abstract

Background: We studied ability of serum cotinine and detailed history of smoking to predict bronchial obstruction. Methods: The baseline study was done during the Mini-Finland Health Survey in 1980 and the follow-up study during the Health 2000 Survey in 2000 for a total of 662 persons free from bronchial obstruction at baseline. Spirometric values of the ratio of forced expiratory volume in one second to forced vital capacity (FEV%) <80% were defined as moderate and <70% as severe bronchial obstruction at follow-up. Cotinine was determined from frozen serum samples collected at baseline. Results: For those who reported at baseline not to smoke currently but whose serum cotinine (≥100 μg/l) indicated active smoking, the age- and sex-adjusted odds ratio of bronchial obstruction at follow-up was 2.55 (95% CI 1.26—5.19) compared with the ‘‘true non-smokers’’ (<100 μg/l). Among current smokers, after adjustment for age, sex, pack years, daily consumption of cigarettes, and inhalation of smoke, the odds ratio of moderate and severe bronchial obstruction was 1.61 (95% CI 1.12— 2.32) and 1.97 (95% CI 1.10—3.54) per an increment of one standard deviation (367 μg/l) in serum cotinine. The predictive value of all the interview measures of past or current smoking was clearly lower. Conclusions: Serum cotinine concentration is a useful predictor for development of obstruction. Smoking history alone may be insufficient in risk factor studies focusing on smoking-related diseases.