Receiver operating characteristic curve analysis (Figure 4c,d) identified a cut‐off value of KL‐6 of 248.3 U/mL (SE 61.5% and SP 73%) in BAL and 1038 U/mL (SE 73.5% and SP 60%) in serum for distinguishing IPF and non‐IPF patients. Here, MUC1 is linked to idiopathic interstitial pneumonia.