Exhaled carbon monoxide in lung disease

To the Editor: We read with interest the paper by Zetterquist et al. 1 in which the levels of exhaled nitric oxide (NO) and carbon monoxide (CO) were measured in a group of asthmatic and cystic fibrosis (CF) patients using two different methods. A new fast-response nondisperse infrared (NDIR) CO analyser was used alongside the old electrochemical method and the results obtained with the two methods were compared. Surprisingly, contrary to what has previously been shown by our own and other groups 2–6, as shown by both methods, the levels of exhaled CO were found to be similar in a group of asthmatic patients and patients with CF compared with normal subjects. The authors conclude that exhaled CO …