MUC1 and idiopathic interstitial pneumonia: The other study, with a larger group of 219 patients with idiopathic interstitial pneumonias (IIPs) and CTD-ILD, also identified a baseline serum KL-6 level of 1000 U/mL as the most discriminatory cut-off value in predicting mortality (sensitivity 67.2%, specificity 60.2%) [35].