MUC1 and idiopathic pulmonary fibrosis: Though it has been reported that serum LDH (cutoff value: 280 IU/L), KL-6 (cutoff value: 1000 IU/L), P/F ratio (cutoff value: 100), and extent of abnormal HRCT findings were significant predictors of 3-month mortality in IPF patients with an AE, we often saw patients with a poor prognosis despite a normal KL-6 level at the time of AE diagnosis [11, 12].