ABSTRACT
BACKGROUND: Exhaled carbon monoxide (CO(Exh)) measurement is used to confirm smoking status in smoking cessation programs, but the cut-off level is still a matter for discussion. The objective of this study was to compare CO(Exh) levels in smokers and non-smokers to validate the method in a Brazilian population and to estimate the probability of the patient still smoking according to different cut-off points. METHODS: In this cross-sectional study we studied non-atopic Caucasian volunteers with no respiratory infection or steroid therapy in the preceding four weeks. Exclusion criteria were: pregnancy; breast feeding; age<18 and >65 years old; and subjects not signing informed consent. Participants filled out a questionnaire and had their CO(Exh) levels measured. Bayes' theorem was used to calculate the posttest probabilities. RESULTS: We included 393 subjects of whom 239 (61%) were smokers. The mean CO(Exh) was 14.7 +/- 9.4 ppm and 4.3 +/- 2.5 ppm (p<0.001) in smokers and nonsmokers, respectively. Patients with CO(Exh) below 8 ppm had a likelihood ratio below 1 of still smoking. The levels 9 ppm and 10 ppm provided likelihood ratios of 1.50 and 1.93, respectively. Better discriminant power was obtained at >11 ppm, when the likelihood ratio became 63.80 (95%CI 16.1-253.1). CONCLUSIONS: In smoking cessation practice, a likelihood ratio approach may be useful to determine the probability that an individual is still smoking according to various CO(Exh) cut-off points instead of using a fixed value for all patients.
Subject(s)
Carbon Monoxide/analysis , Smoking Cessation , Smoking/metabolism , Adult , Bayes Theorem , Biomarkers/analysis , Brazil , Breath Tests , Cross-Sectional Studies , Female , Humans , Male , Reference Values , Surveys and QuestionnairesABSTRACT
AIMS: To study tobacco abstinence and risk factors for failure in smoking cessation program and to evaluate the need for special strategies in a Brazilian cohort of smokers. DESIGN: A non-randomized, prospective, open clinical trial. PATIENTS AND METHODS: We studied smokers who attended the Smoking Cessation Clinics of Hospital Sao Lucas da PUCRS, in Porto Alegre, Brazil between July, 1999 and June, 2003. All participated in the same behavioral therapy program and, according to the Fagerstrom test, also received nicotine patches and/or bupropion. Sustained abstinence was confirmed by exhaled CO measurements
