Background: Serum Krebs von den Lungen-6 (KL-6) has been reported to be elevated in patients with idiopathic pulmonary fibrosis (IPF).Objective: The aim of this study was to evaluate the diagnostic value of KL-6 and whether the expression value of KL-6 could indicate the severity of the disease in IPF patients. To address this question, it is necessary to see whether the patients' physical characteristics and other clinical conditions could affect the baseline KL-6 level.