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

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 (<10 ppm) that also met lower thresholds was calculated for each unit change from <9 ppm to <2 ppm. Additionally, associations of established predictors with outcome were assessed in logistic regressions for selected thresholds. Results: At <10 ppm, 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. <8 ppm: 34.7% success), but at <3 ppm, only 26.3% would still be regarded as successful. With the threshold reduced to <3 ppm established predictors of cessation showed a weaker association with outcome than with the threshold at <10 ppm 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. (C) 2013 Elsevier Ltd. All rights reserved.