SPP1 and idiopathic pulmonary fibrosis: Higher levels of OPN in IPF patients with acute exacerbation than stable IPF patients and controls and higher levels in stable IPF patients than controlsNo correlation between OPN levels and FVC and DLCOPrediction of the risk of mortality by OPN levels higher than 3.24 ng/mL with a sensitivity of 57.1% and a specificity of 77.1%High levels of OPN are an independent risk factor for mortality