Interstitial lung disease (ILD) is a heterogeneous parenchymal disorder.1 2 Patients with ILD often present with non-specific symptoms such as a non-productive cough and exertional dyspnoea. The differential diagnosis for ILD is broad and includes conditions such as connective tissue disease (CTD), hypersensitivity pneumonitis, drug-associated ILD and granulomatous diseases. Furthermore, the initial management depends on factors such as antigen exposure, causative drugs, inflammation and fibrosis. Accurate diagnosis requires a detailed medical history, chest high-resolution CT (HRCT) and pathology.3 4

From a physiological perspective, ILD manifests as a restrictive disorder with reduced diffusion capacity of the lungs for carbon monoxide (DLco).5–7 Many clinical trials on ILD have used forced vital capacity (FVC) as a surrogate marker for mortality.8 9 Additionally, trends in FVC and DLco have been shown to be useful predictors of mortality, particularly in idiopathic pulmonary fibrosis (IPF).10 11 In the management and prognosis of ILD, pulmonary function tests (PFT), including FVC and DLco, are crucial physiological indices.12–14 It is important to note that height, …