To the Editors:
We read with great interest the study by Bridevaux et al. 1 about the possible sex role in weight gain and faster forced expiratory volume in 1 s (FEV1) decline as predictors of systemic inflammation (measured by C-reactive protein (CRP) levels) in chronic obstructive pulmonary disease (COPD) patients. Although the article is interesting, we found some conflicting methodological aspects that we wanted to highlight.
First, the authors state that females with COPD have a worse prognosis than males, based on the only study that supports this statement in the literature. Indeed, there is a body of literature indicating that females with COPD have better outcomes than males, especially those receiving long-term oxygen therapy 2. In an attempt to clarify this, in the March issue of the European Respiratory Journal, we published the results of a study of 265 females and 272 males with COPD matched by disease severity (according to percentage FEV1 and BODE (body mass index, airflow obstruction, dyspnoea and exercise capacity index), in which we showed that females live longer than males 3. Secondly, the diagnosis of COPD (also used in the study title) is not totally accurate because the authors use pre-bronchodilator spirometry. The European Respiratory Society/American Thoracic Society recommendations clearly state that, to properly diagnose COPD, a post-bronchodilator FEV1 value must be used. The literature suggests that 30–40% of patients with pre-bronchodilator airflow obstruction correct after a bronchodilator is given.
The lack of precise diagnosis is important for many reasons. 1) The correct classification of the population as having COPD may be wrong. If we consider only those in Global Initiative for Chronic Obstructive Lung Disease stages 2–4 (those that usually express a more important systemic component), just 71 females were included, a number that may preclude a robust analysis. Based on this first point, we believe that the title of the article is not appropriate and should be restricted to the relationship between CRP and lung function. 2) The analysis of FEV1 decline may be influenced by the degree of untested reversibility because the presence of bronchial reactivity is a well-known factor affecting lung function decline. 3) The degree of bronchial responsiveness also affects the level of CRP values, because it has been shown that a positive bronchodilation response is associated with a higher systemic inflammatory response 4. We previously analysed the relationship between CRP levels and clinical characteristics in COPD patients 5, and cross-sectionally described the inverse and direct relationships between FEV1 and body mass index, respectively, with CRP levels.
Lastly, we do not believe that one can accurately describe FEV1 decline when only two points are being followed, especially when that decline is then related to the CRP change. Usually, at least three follow-up points are necessary to precisely determine the slope of the change in a variable.
Although we acknowledge the important message that the study by Bridevaux et al. 1 has in the field of proposing mechanistic effects for the systemic inflammatory response in COPD patients, we believe these important issues should be clarified so that the findings can be placed in the appropriate context.
Statement of interest
None declared.
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