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.
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.
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.