Consequently, we have revealed the following three major characteristics of monomeric periostin: (1) it has the greatest ability to diagnose IPF comparable with KL-6 and SP-D compared to total periostin; (2) it is able to predict the short-term progression of IPF comparable with total periostin; and (3) it has a high ratio to total periostin in IPF compared to other periostin-high diseases. The gene discussed is MUC1; the disease is idiopathic interstitial pneumonia.