SFTPD and hypersensitivity pneumonitis: Although our results indicate that SP-D is a potential biomarker for assessing disease status in patients with ILD, the restricted number of included studies hinders us from delineating the role of SP-D in different types of ILD through subgroup analyses, such as CTD-ILD, granulomatous pneumonia, sarcoidosis, and hypersensitivity pneumonitis.