Serum PRDX4 protein levels at AE-IPF were significantly higher than those at S-IPF (p <  0.05) (Fig. 2a); however, serum KL-6, SP-D, and LDH levels showed no significant changes (Figs. 2b, c, and d). This evidence concerns the gene PRDX4 and idiopathic pulmonary fibrosis.