MUC1 and interstitial lung disease: In addition to the comparisons of the KL-6 levels between the survivors and nonsurvivors, the highest KL-6 levels in ELF and serum among the series of measurements were compared between the patients with primary (n = 20) and secondary (n = 12) ARDS or between the patients with (n = 3) and without (n = 29) preexisting interstitial lung disease (ILD).