title: The effect of reducing the threshold for carbon monoxide validation of smoking abstinence--evidence from the English Stop Smoking Services.
abstract: BACKGROUND
  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.
authors.affiliation: National Centre for Smoking Cessation and Training & Clinical, Educational and Health Psychology, University College London, UK. l.brose@ucl.ac.uk
authors.forename: Leonie S
authors.initials: LS
authors.lastname: Brose
authors.forename: Ildikó
authors.initials: I
authors.lastname: Tombor
authors.forename: Lion
authors.initials: L
authors.lastname: Shahab
authors.forename: Robert
authors.initials: R
authors.lastname: West
mesh_terms: D015415:Biomarkers / Q000378:metabolism; D001944:Breath Tests; D002248:Carbon Monoxide / Q000032:analysis*; D004739:England; D006801:Humans; D016015:Logistic Models; D017063:Outcome Assessment, Health Care / Q000379:methods / Q000706:statistics & numerical data*; D011314:Preventive Health Services; D012680:Sensitivity and Specificity; D012907:Smoking / Q000378:metabolism; D016540:Smoking Cessation / Q000379:methods / Q000706:statistics & numerical data*; D000074606:Smoking Prevention
chemical_list: D015415:Biomarkers; D002248:Carbon Monoxide
keywords: Carbon monoxide; Outcome criteria; Smoking cessation; Success rates