Cut-off value of FEV(1)/FEV(6) as a surrogate for FEV(1)/FVC for detecting airway obstruction in a Korean population

BACKGROUND: Forced expiratory volume in 1 second (FEV(1))/forced expiratory volume in 6 seconds (FEV(6)) has been proposed as an alternative to FEV(1)/forced vital capacity (FVC) for detecting airway obstruction. A fixed cut-off value for FEV(1)/FEV(6) in a Korean population is lacking. We investigated a fixed cut-off for FEV(1)/FEV(6) as a surrogate for FEV(1)/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 FEV(1)/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 FEV(1)/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 FEV(1)/FVC <70%. Optimal FEV(1)/FEV(6) cut-off for predicting FEV(1)/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 FEV(1)/FEV(6) 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 FEV(1)/FVC < lower limit of normal, FEV(1)/FEV(6) <75% tended to over-diagnose airflow limitation (just like a fixed cut-off of FEV(1)/FVC <70%). When grouped according to age and FEV(1) (%), FEV(1)/FEV(6) <75% diagnosed more airway obstruction in older participants and mild–moderate stages compared with FEV(1)/FVC <70%. CONCLUSION: A valid fixed cut-off for detecting airway obstruction in a Korean population is FEV(1)/FEV(6) of 75%, but should be used with caution in older individuals and those with mild–moderate airway obstruction.