Age-related changes in the respiratory function of healthy adults are important factors to be considered. With increasing age, there is a reduction in lung elastic recoil and respiratory muscle strength, which results in increased residual volume (RV). RV increases by approximately 50% between the ages of 20 and 70 years.2 Total lung capacity remains relatively unchanged with increasing age.3 Therefore, the ratio of RV to total lung capacity increases with age. Observations in the present study regarding the FEV3/FVC ratio are similar to age-related changes in lung function. It has also been observed that the utility of FEV1/FVC ratio in the diagnosis of airflow obstruction, especially in older individuals, is limited and can lead to overdiagnosis of COPD.4 The mean age of patients with isolated FEV3/FVC reduction in the present study was 61.2 ± 12.3 years. Therefore, calculating the sensitivity and specificity of the FEV3/FVC ratio using the FEV1/FVC ratio as the gold standard for airway obstruction may be inappropriate in older patients.