Furthermore, multivariate analysis using stratified Cox proportional hazard regression model by ILD-GAP index identified SFTPB level in serum EVs as an independent prognostic factor from smoking history and ILD-GAP index (HR 2.65; 95%CI 1.04–6.74; P = 0.041) (Table 2). Here, SFTPB is linked to interstitial lung disease.