AIMS: The definition of limited airflow as forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC) ratio for chronic obstructive pulmonary disease (COPD) is still controversial. The objective of this study was to compare the prevalence of COPD using fixed ratio and lower limit of normal (LLN) of FEV1/FVC for the presence of airflow limitation and evaluate the performance of FEV1/forced expiratory volume in 6 s (FEV6) in patients diagnosed with COPD according to the Global Initiative for Chronic Obstructive Lung Disease (GOLD) fixed ratio. SUBJECTS AND
METHODS: Patients who presented to the pulmonary disease clinic between May 2008 and December 2017 and who were diagnosed with COPD were evaluated retrospectively. The distribution of FEV1/FVC-LLN according to the GOLD fixed ratio was evaluated after the patients were divided based on age groups. A receiver operating characteristics curve was used to determine the best FEV1/FEV6 cutoff value which fit into the FEV1/FVC RESULTS: Of the patients, 165 (85.9%) were male and 27 were female, with a mean age of 64.40 ± 10.66 years (range, 40–85). Among the patients, 11.5% of 61 patients aged 40–60 years, 28.4% of 67 patients aged 61–70 years, and 26.6% of 64 patients aged over 70 years were out of the diagnosis of obstruction according to the fixed ratio of FEV1/FVC >LLN. The cutoff value of FEV1/FEV6 for airway obstruction according to FEV1/FVC CONCLUSIONS: In this study, older patients, particularly, were diagnosed less often with an FEV1/FVC