Introduction: Forced expiratory value in one score  (FEV1)/ Forced vital capacity (FVC) was used in classical literature for primary classifications of pulmonary disorders. American Thoracic Society/ European Respiratory Society guidelines recommended using FEV1/VC instead of FEV1/FVC.The aim of study was determination of the extent of superiority of FEV1/VC over the FEV1/FVC.
Materials and Methods: Two hundred seven subjects whom suffered from different pulmonary disorders were evaluated by standard spirometry, lung volume and Carbon mono-oxide lung diffusion capacity (DLCO). Accuracy of FEV1/VC and FEV1/FVC for diagnosing lung disease was compared by area under the ROC curve, sensitivity and specificity analysis including Kraemer efficiency and likelihood ration methods. Gold standards were diagnosis confirmed by over-all clinical and para-clinical judgment.
Results: Primary classification of FEV1/FVC and FEV1/VC according to gold standards showed that FEV1/FVC detected obstructive and restrictive lung disease better than FEV1/VC. FEV1/FVC was able to detect the obstructive and restrictive lung disease correctly in 61% and 34% and FEV1/VC in 56% and 33% respectively. FEV1/FVC showed 100% agreement with forced expiratory flow (FEF)=25-75%,   and Maximum expiratory flow (MEF)=50% but this agreement for FEV1/VC was 95-96%. Accuracy assessments revealed the superiority of FEV/FVC in the likelihood ratio method. Also, based on the ROC curve and Kraemer’s coefficient, more accurate results were obtained by FEV1/FVC, compared to FEV1/VC.
Conclusion: FEV1/FVC showed marginally higher accuracy for detecting lung disease than FEV1/VC.