MUC1 and acute respiratory distress syndrome: This observation was supported by the following study results: KL-6 levels in ELF were significantly elevated in the nonsurvivors on days 0 to 3 after the diagnosis of ARDS compared to the survivors, and the patients with KL-6 levels in ELF higher than 3453 U/mL had significantly poorer prognosis than those with lower KL-6 levels in ELF.