The effect of reducing the threshold for carbon monoxide validation of smoking abstinence--evidence from the English Stop Smoking Services

Addict Behav. 2013 Oct;38(10):2529-31. doi: 10.1016/j.addbeh.2013.04.006. Epub 2013 May 7.


Introduction: The most commonly used threshold of expired-air carbon monoxide (CO) concentration to validate self-reported smoking abstinence is <10 parts per million (ppm). It has been proposed to reduce this threshold. This study examined what effect a reduction would have on short-term success rates in clinical practice.

Methods: A total of 315,718 quit attempts supported by English NHS Stop Smoking Services were included in the analysis. The proportion of 4-week quits as determined by the Russell standard (<10ppm) that also met lower thresholds was calculated for each unit change from <9ppm to <2ppm. Additionally, associations of established predictors with outcome were assessed in logistic regressions for selected thresholds.

Results: At <10ppm, 35% of quit attempts were regarded as successful. Differences for a single unit reduction increased with each reduction; small reductions had very little impact (e.g. <8ppm: 34.7% success), but at <3ppm, only 26.3% would still be regarded as successful. With the threshold reduced to <3ppm established predictors of cessation showed a weaker association with outcome than with the threshold at <10ppm suggesting an increase in error of outcome measurement.

Conclusions: Reducing the threshold for expired-air CO concentration to validate abstinence would have a minimal effect on success rates unless the threshold were reduced substantially which would likely increase error of measurement.

Keywords: Carbon monoxide; Outcome criteria; Smoking cessation; Success rates.

MeSH terms

  • Biomarkers / metabolism
  • Breath Tests
  • Carbon Monoxide / analysis*
  • England
  • Humans
  • Logistic Models
  • Outcome Assessment, Health Care / methods
  • Outcome Assessment, Health Care / statistics & numerical data*
  • Preventive Health Services
  • Sensitivity and Specificity
  • Smoking / metabolism
  • Smoking Cessation / methods
  • Smoking Cessation / statistics & numerical data*
  • Smoking Prevention*


  • Biomarkers
  • Carbon Monoxide