PRDX4 and idiopathic pulmonary fibrosis: The molecular weight of these biomarkers is smaller than that of KL-6 (> 200 kDa) [31], and considering that the molecular weight is associated with biomarker profiles [10, 29], the small molecular weight of PRDX4 (34 kDa) [20] may explain its better profile as a marker for detecting AE-IPF.