SFTPD and idiopathic pulmonary fibrosis: In the unadjusted Cox analysis, higher baseline GAP stage (≥II), higher serum SP-D level (≥194.7 ng/mL), and higher eosinophil percentage (≥3.21 %) in BAL fluid samples were significant prognostic factors for IPF (HR [95 % CI], 4.02 [1.68–9.64], 3.49 [1.36–8.94], and 2.42 [1.03–5.68], respectively).