MUC1 and idiopathic pulmonary fibrosis: However, there was no statistically significant difference in serum KL-6 levels between ASSD-ILD+ patients and IPF patients (1653.56 ± 1165.19 U/mL vs. 1682.23 ± 949.93 U/mL, p = 0.14, Fig. 1b).