| Summary: | Kyung Soo Chung,1,2 Ji Ye Jung,1,2 Moo Suk Park,1,2 Young Sam Kim,1,2 Se Kyu Kim,1,2 Joon Chang,1,2 Joo Han Song1,2 1Division of Pulmonology, Department of Internal Medicine, Yonsei University College of Medicine, Seoul, Republic of Korea; 2Institute of Chest Disease, Severance Hospital, Yonsei University College of Medicine, Seoul, Republic of Korea Background: Forced expiratory volume in 1 second (FEV1)/forced expiratory volume in 6 seconds (FEV6) has been proposed as an alternative to FEV1/forced vital capacity (FVC) for detecting airway obstruction. A fixed cut-off value for FEV1/FEV6 in a Korean population is lacking. We investigated a fixed cut-off for FEV1/FEV6 as a surrogate for FEV1/FVC for detecting airway obstruction.Materials and methods: We used data obtained in the 5 years of the Fifth and Sixth Korean National Health and Nutrition Examination Survey. A total of 14,978 participants aged ≥40 years who underwent spirometry adequately were the study cohort. “Airway obstruction” was a fixed cut-off FEV1/FVC <70% according to the Global Initiative for Chronic Obstructive Lung Disease guidelines. We also used European Respiratory Society/Global Lung Initiative 2012 equations for the FEV1/FVC lower limit of normal.Results: Among the 14,978 participants (43.5% male, 56.5% female; mean age: 56.9 years for men and 57.0 years for women), 14.0% had obstructive lung function according to a fixed cut-off FEV1/FVC <70%. Optimal FEV1/FEV6 cut-off for predicting FEV1/FVC <70% was 75% using receiver operating characteristic curve analyses (area under receiver operating characteristic curve =0.989, 95% confidence interval 0.987–0.990). This fixed cut-off of FEV1/FEV6 showed 93.8% sensitivity, 94.8% specificity, 74.7% positive predictive value, 98.9% negative predictive value, and 0.8 Cohen’s kappa coefficient. When compared with FEV1/FVC < lower limit of normal, FEV1/FEV6 <75% tended to over-diagnose airflow limitation (just like a fixed cut-off of FEV1/FVC <70%). When grouped according to age and FEV1 (%), FEV1/FEV6 <75% diagnosed more airway obstruction in older participants and mild–moderate stages compared with FEV1/FVC <70%.Conclusion: A valid fixed cut-off for detecting airway obstruction in a Korean population is FEV1/FEV6 of 75%, but should be used with caution in older individuals and those with mild–moderate airway obstruction. Keywords: chronic obstructive pulmonary disease, forced expiratory volume in 6 seconds, pulmonary function test, airway obstruction
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