This prospective study measured serum monomeric and total periostin, Klebs von den Lungen-6 (KL-6), surfactant protein D (SP-D), and lactate dehydrogenase (LDH) in 19 patients with RA-ILD, 20 RA without ILD, and 137 healthy controls (HC). The gene discussed is MUC1; the disease is interstitial lung disease.