Defining obstruction in COPD: do fixed ratio and lower limit of normal criteria reflect different clinical characteristics? findings from a Greek cross-sectional study (EMENO)

BACKGROUND AND OBJECTIVES: In epidemiological research, spirometry is commonly used to estimate prevalence of COPD, as reliance on imprecisely delineated symptoms may introduce bias. Actually, the prevalence of airflow limitation in adults with no prior asthma diagnosis was studied using two different cut-offs for the FEV₁/FVC ratio: the fixed ratio (FR) and the lower limit of normal (LLN), based on data from the EMENO survey. Our objective was to estimate COPD prevalence in Greece under both definitions and to compare associated clinical features and comorbidities. METHODS: The EMENO study was a population-based survey (2014–2016) of 6,006 adults (≥18 years). This analysis included 2,450 participants aged 30–91 years, with high-quality spirometry and no prior asthma diagnosis. Airflow limitation indicative of COPD was defined by pre-bronchodilator FEV1/FVC < 0.70 (FR) and FEV1/FVC < LLN; self-reported COPD (SRPD) was also analyzed. Comorbidities and demographics were assessed through interviews and medical exams. RESULTS: COPD prevalence was 8.51% (FR), 5.33% (LLN), and 1.97% (SRPD). It was more common in men (13.2% FR+ and 8.5% LLN+), with the highest prevalence among current smokers (11.6%, FR; 9.1%, LLN). Prevalence was also higher in participants reporting respiratory symptoms. The FR+/LLN− (discordant) group was strongly associated with older age, blue-collar occupations, and comorbidities. Concordant cases (FR+/LLN+) had a higher prevalence of smoking and respiratory symptoms compared to discordant cases. Obesity was inversely associated with COPD under the LLN criterion, while sleep apnea syndrome increased the odds of concordant COPD. CONCLUSION: COPD prevalence in Greece differed according to the obstructive threshold applied, with discordant and concordant cases showing distinct demographic and clinical risk profiles. The higher prevalence of obstruction among symptomatic participants further supports the use of spirometry as a valid surrogate in epidemiological studies. Overall, reliance on a single definition may misrepresent the true burden and heterogeneity of the disease.