The purpose of the study is to evaluate the significance of KL-6 as a biomarker in the clinical diagnosis of interstitial lung disease (ILD) by detecting serum KL-6 levels among patients with ILD, and comparing them to the clinical diagnostic criteria and other respiratory diseases. In addition, the study discusses the value of KL-6 levels in terms of ILD treatment effect evaluation through the detection of serum KL-6 levels before treatment and after treatment.