MUC1 and interstitial lung disease: <h4>Objective</h4>This study aimed to assess the clinical value of cytokeratin 19 fragment (CYFRA21-1) and its correlation with Krebs von den Lungen-6 (KL-6) in stratifying the severity of rheumatoid arthritis-associated interstitial lung disease (RA-ILD).<h4>Methods</h4>Data were retrospectively collected from 178 patients with rheumatoid arthritis (RA) admitted to our hospital between November 2024 and September 2025.