Median serum MUC5B protein levels were 16.62 ng/mL (IQR, 12.57 to 21.48 ng/mL) in healthy controls, 19.68 ng/mL (IQR, 15.75 to 27.67 ng/mL) in CTD-non ILD, and 23.25 ng/mL (IQR, 17.84 to 35.70 ng/mL) in CTD-ILD. Here, MUC5B is linked to interstitial lung disease.