S100A9 and idiopathic pulmonary fibrosis: According to the unadjusted ROC-AUC analysis, the percentage of S100A9+CD163− cells (Gate 1) showed the best diagnostic value for IPF (ROC-AUC 0.802, 95% CI [0.687–0.928]) and was a significantly better biomarker to discriminate IPF from iNSIP than serum SP-D (0.616, 95% CI [0.446–0.786]) (p < 0.05, Fig. 2).