Breath carbon monoxide as an indication of smoking habit

Chest. 2000 Mar;117(3):758-63. doi: 10.1378/chest.117.3.758.


Study objective: To assess whether the breath carbon monoxide (CO) concentration can be used to determine a patient's smoking habits in a respiratory outpatient clinic.

Design: To provide a normal range for smokers and nonsmokers, 41 outpatients and 24 healthy subjects were questioned on their smoking habits and asked to provide two breaths into a CO monitor (EC50 Smokerlyser; Bedfont Instruments; Kent, UK). In a subsequent single-blind study, 51 different outpatients were not told of the purpose of the study and were assessed by extensive questionnaire, spirometry, and Smokerlyser estimation.

Setting: The Chest Clinic and Pulmonary Medicine Department at the Northern General Hospital, Sheffield, UK.

Participants: Phase 1 involved 41 outpatients attending the Chest Clinic and 24 nonoutpatient colleagues. In phase 2, an additional 51 different outpatients were studied.

Measurements and results: The mean (SD) breath CO levels were 17.4 (11.6) parts per million (ppm) for smokers and 1.8 (1.3) ppm for nonsmokers (p < 0.001). A level of 6 ppm was taken as the cutoff, as this gave a selectivity of 96% and a sensitivity of 94% for outpatients. Of the 51 study patients, 5 admitted to smoking in the administered questionnaire. Eight denied smoking but had a mean breath CO > 6 ppm (7.5 to 42 ppm). Of these, three admitted to smoking after being explained the implication of the reading.

Conclusions: Breath CO concentration provides an easy, noninvasive, and immediate way of assessing a patient's smoking status. A reading > 6 ppm strongly suggests that an outpatient is a smoker.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Breath Tests*
  • Carbon Monoxide / analysis*
  • Carboxyhemoglobin / analysis
  • Female
  • Humans
  • Male
  • Middle Aged
  • Reference Values
  • Sensitivity and Specificity
  • Smoking / adverse effects
  • Smoking / physiopathology*
  • Spirometry


  • Carbon Monoxide
  • Carboxyhemoglobin