[Cigarette smoking among adolescents. Estimated prevalence by a questionnaire and serum cotinine]. / Tabaquismo en adolescentes. Prevalencia estimada mediante declaración y cotinina sérica.

BACKGROUND: The tobacco smoking epidemic is causing more deaths than anyone before. Young population is the main aim of tobacco advertisements. We estimated the prevalence of tobacco use among adolescents and their environment, the agreement of questionnaire and serum cotinine and the total prevalence of exposure (active plus pasive). SUBJECTS AND METHODS: Cross-sectional study in 439 highschool students. We obtained a blood sample and anonimously inquired about their tobacco consumption and the existence of smokers in their environment. We analized the agreement between both methods. RESULTS: 56% have ever smoked tobacco. Declared prevalence of consumption was 34% (CI95%= 29.49-38.51), being 40% among girls and 23% among boys. The agreement between cotinine and declaration was high only in voluntary smokers (Kappa = 0.68 for 1 o more cigarettes/day and Kappa = 0.76 for 10 or more cigarettes/day). Smoking prevalence of the famliy, friends and school among smokers was higher (80%, 71% and 88%, respectively) than among non smokers (65%, 24% and 78%). Combining questionnaire and cotinine it was estimated that total prevalence of exposure was larger than 64%. CONCLUSIONS: The high prevalence of exposure and the asociation of tobacco smoking among adolescents and their environment demands an educational program against tobacco including family, social and school environments. The agreement between declaration and serum cotinine is high only when consumption is daily.