Exhaled carbon monoxide in COPD.

I read with interest the article by Montuschi et al (August 2001).1 However, their study design might not be appropriate. The number of ex-smokers (n 15) is too small. According to Figure 1 in their article, only 2 of 15 ex-smokers showed high exhaled carbon monoxide. It is well known that some ex-smokers deceive doctors about their smoking. Montuschi et al1 mentioned that smoking habit was checked by the measurement of urinary cotinine levels (data not shown). But it is not enough. The measurement of carboxyhemoglobin (COHb) concentration in blood is an effective means of ascertaining the smoking status of patients.2 They should have checked the blood COHb concentrations of the subjects. If those two ex-smokers with high exhaled carbon monoxide levels showed high COHb, they were deceivers.