Pulmonary function tests (PFTs) provide the useful information about detection as well as characteristics or severity of lung disease. Forced vital capacity (FVC) have played an important role for the diagnosis of idiopathic pulmonary fibrosis (IPF) for many years. Patients can be diagnosed as interstitial lung disease if percent vital capacity (%VC) is lower than 80 %. It also correlates with a poor outcome in patient with IPF [1,2]. Forced expiratory volume in one second (FEV1) is also an important predictor in PFTs, especially for screening of chronic obstructive pulmonary disease (COPD).