title: Cut-off levels for breath carbon monoxide as a marker for cigarette smoking.
abstract: OBJECTIVE
  Current clinical studies often use a breath carbon monoxide (BCO) cut-off level of 8 parts per million (p.p.m.) or higher to identify smoking. In this study, the cut-off level of BCO as an indicator of smoking over the past 24 hours was re-examined.
  
  
  METHODS
  BCO and self-reported smoking were obtained each weekday for up to 14 weeks in 213 subjects paid to deliver reduced BCO values. Analysis of 12 386 paired values for reported smoking and BCO were analyzed.
  
  
  RESULTS
  The 25% quartile, median and 75% quartile values for BCO were 1, 1 and 2 p.p.m. on non-smoking days and 2, 5 and 12 p.p.m. on smoking days, respectively. Receiver-operating characteristic (ROC) analysis indicated that BCO provided high diagnostic accuracy to distinguish between smoking and non-smoking days [area under the curve (AUC) = 0.853, P < 0.0001]. The highest combined sensitivity and specificity was observed at a BCO cut-off level of 3 p.p.m. (sensitivity = 71.5%; specificity = 84.8%). At a BCO cut-off of 8 p.p.m. sensitivity and specificity were 40.6% and 98.2%, respectively, indicating that many smokers would be falsely classified as abstinent. Finally, the percentage of true tests (positive and negative) was highest at a BCO cut-off of 2 p.p.m. (80.2%).
  
  
  CONCLUSIONS
  BCO cut-off levels well below 8 p.p.m and as low as 2-3 p.p.m. may be more useful when it is important to maximize identification of smoking abstinence with a high degree of certainty.
authors.affiliation: Department of Psychiatry, University of Texas HSC, San Antonio, Texas 78229, USA. javors@uthscsa.edu
authors.forename: Martin A
authors.initials: MA
authors.lastname: Javors
authors.forename: John P
authors.initials: JP
authors.lastname: Hatch
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Lamb
mesh_terms: D000328:Adult; D000368:Aged; D015415:Biomarkers / Q000032:analysis; D001944:Breath Tests / Q000379:methods; D002248:Carbon Monoxide / Q000032:analysis*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D012016:Reference Values; D012680:Sensitivity and Specificity; D000074606:Smoking Prevention; D014342:Truth Disclosure
chemical_list: D015415:Biomarkers; D002248:Carbon Monoxide