Exhaled carbon monoxide as a marker for evaluating smoking abstinence in a Brazilian population sample

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 post-test probabilities.

Results:

We included 393 subjects of whom 239 (61%) were smokers. The mean CO_Exh was 14.7 +/− 9.4ppm and 4.3 +/− 2.5ppm (p<0.001) in smokers and non-smokers, respectively. Patients with CO_Exh below 8ppm had a likelihood ratio below 1 of still smoking. The levels 9ppm and 10ppm provided likelihood ratios of 1.50 and 1.93, respectively. Better discriminant power was obtained at >11ppm, 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 COExhCO_Exh cut-off points instead of using a fixed value for all patients.

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