Affiliations: The Japanese Red Cross Hiroshima College of Nursing Hiroshima, Japan,
Catholic University Sacred Heart Rome, Italy
Correspondence to: Hiroshi Kawane, MD, PhD, FCCP, The Japanese Red Cross Hiroshima College of Nursing, 1-2 Ajinadai-higashi, Hatsukaichi City, Hiroshima 738-0052, Japan; e-mail: firstname.lastname@example.org
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.
Regarding the comment by Hiroshi Kawane, I would like to make the following points:
1. Measurement of urinary cotinine is a well-accepted method to assess smoking exposure.1–2 Measurement of carboxyhemoglobin may be helpful, but it is not necessary for excluding smoking exposure.
2. Patients with the highest exhaled carbon monoxide values had a negative urinary cotinine test result, indicating that they were not exposed to smoking. The high carbon monoxide values are likely to reflect the interindividual biological variability.
3. Even taking out the two highest exhaled carbon monoxide values, the difference between healthy nonsmokers and COPD patients who were ex-smokers is still significant (3.1 ± 0.3 ppm vs 4.7 ± 0.4 ppm, p < 0.01).
4. We do not agree that the study design was not appropriate. It was a cross-sectional study including 15 patients who were ex-smokers. The number was small, but sufficient to detect differences.
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