The areas under the ROC curves of serum GDF-15 levels were statistically significant in the classification of AE-IPF (n = 47) or S-IPF patients (n = 61) (ROC: 0.738, p < 0.001, 95% CI: 0.529-0.809, cut-off value 989.3 pg/ml) (Figure 3A). This evidence concerns the gene GDF15 and idiopathic pulmonary fibrosis.