Cut-off value of FEV1/FEV6 as a surrogate for FEV1/FVC for detecting airway obstruction in a Korean population

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.