Background and objective: There is increasing recognition of asthma–COPD overlap syndrome (ACOS), which shares some features of both asthma and COPD; however, the prevalence and characteristics of ACOS are not well understood. The aim of this study was to investigate the prevalence of ACOS among patients with COPD and its characteristics using a stepwise approach as stated in the recent report of the Global Initiative for Asthma (GINA) and the Global Initiative for Chronic Obstructive Lung Disease (GOLD).
Methods: This multicenter, cross-sectional, observational study enrolled outpatients who were receiving medical treatment for COPD. Clinical data, including spirometry results, were retrieved from medical records. For symptom assessment, patients were asked to complete the Clinical COPD questionnaire and the modified British Medical Research Council questionnaire.
Results: Of the 1,008 patients analyzed, 167 (16.6%) had syndromic features of ACOS. Of the total number of patients, 93 and 42 (9.2% and 4.2%) also had a predefined clinical variability of ≥12%/≥200 mL and ≥12%/≥400 mL in forced expiratory volume in 1 second (FEV₁), respectively, and therefore were identified as having ACOS. Conversely, the number of patients who had either syndromic or spirometric feature of ACOS was 595 (59.0%, ≥12%/≥200 mL FEV₁ clinical variability), and 328 patients (32.5%, ≥12%/≥400 mL FEV₁ clinical variability) had both the features. Patients identified as having ACOS were of significantly younger age, had a shorter duration of COPD, lower number of pack-years, better lung function, milder dyspnea symptoms, and higher peripheral blood eosinophil values compared with patients with COPD alone. The rate of exacerbations in the previous year was not significantly different between the ACOS and COPD groups.
Conclusion: Using a stepwise approach, as stated in the GINA/GOLD report, the proportions of patients identified as having ACOS were found to be 9.2% and 4.2% (depending on the FEV₁variability cutoff used) among the 1,008 outpatients medically treated for COPD in a real-life clinical setting.

Keywords: obstructive lung diseases, airway hyperresponsiveness, respiratory function tests, differential diagnosis

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