SPP1 and idiopathic pulmonary fibrosis: A study performed on a small cohort of 32 patients with acute exacerbation of IPF (AE-IPF), 39 patients with stable IPF (S-IPF), and 20 control subjects demonstrated that serum SPP1 concentrations in patients with AE-IPF significantly increased compared to the S-IPF patients or control subjects, suggesting that OPN is a potential biomarker for monitoring the onset of AE-IPF and a predictor of the survival of patients with IPF [53].