MUC1 and rheumatoid arthritis: Lee et al. also reported that, among 62 RA-UIP patients, those with a high KL-6 level (≥933 U/mL) had a reduced survival (median survival period: 51 vs. 96 months; P = 0.019) than those without a high KL-6 level irrespective of age, sex, and baseline lung function [22].