Breath carbon monoxide as an indication of smoking habit

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

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.

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

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

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.

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.