Diagnostic Performance of Forced Expiratory Volume in Six Seconds for the Detection of Obstructive and Restrictive Pulmonary Diseases in a Population of Young Adults in South of Iran

Background: Forced expiratory volume in 6 seconds (FEV6) is a reliable substitute for forced vital capacity (FVC) to identify pulmonary diseases. This study aimed to determine the diagnostic performance of FEV6 in the detection of obstructive and restrictive spirometric patterns. Methods: In this cross-sectional study, spirometry was performed on patients referred to the occupational medicine clinic of Shahid Mohammadi Hospital, Bandar Abbas, Iran, 2018. Spirometric parameters, including FEV1, FVC, and FEV6, were recorded for those tests meeting the American Thoracic Society (ATS) standards. Taken as the reference, the FEV1/FVC ratio<70% indicated airway obstruction, and the restrictive pattern was defined as FVC<80%. Results: In general, 1100 spirometries were included after meeting the ATS standards. The optimal cut-off of FEV1/FEV6 for the prediction of airway obstruction was 71.45% with a sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and diagnostic accuracy of 97.22%, 98.22%, 89.17%, 99.57%, and 98.09%, respectively. The best cut-off of FEV6 for the prediction of the restrictive pattern was 79.23% with the corresponding diagnostic indices of 97.29%, 99.05%, 94.11%, 99.57%, and 98.81%, respectively. Based on the FEV1/FEV6 cut-off, the frequency of obstruction was 14.27% (157/1100) compared to 13.09% based on FEV1/FVC. The frequency of restriction was 13.90% (153/1100) according to the FEV6 cut-off compared to 13.45% with respect to FVC. Conclusion: Overall, our results indicated the applicability of FEV1/FEV6 as an accepted surrogate for FEV1/FVC to diagnose airway obstruction, particularly to screen for chronic obstructive pulmonary disease (COPD) among high-risk patients. In addition, FEV6 is potentially an appropriate substitute for FVC to detect a restrictive pattern.