SFTPD and interstitial lung disease: Although AE-ILD biomarkers are used in clinical practice, including C-reactive protein (CRP), lactate dehydrogenase (LDH), Krebs von den Lungen-6 (KL-6), and pulmonary surfactant protein D (SP-D), none of these classical markers alone determines the prognosis of AE-ILDs [3].