IL17A and idiopathic pulmonary fibrosis: When differentiating CTD-ILD from IPF, using a cutoff value of 0.596, BAFF and IL-17 combination achieved 84.2% sensitivity and 78.3% specificity (Youden’s index: 0.625, AUC = 0.883, 95% CI = 0.786–0.981), while BAFF alone achieved 69.6% sensitivity and 100% specificity using a cutoff of 1.427 (Youden’s index: 0.696, AUC = 0.926, 95% CI = 0.852–1.000) and IL-17 alone achieved 60.9% sensitivity and 100% specificity using a cutoff of 6.37 (Youden’s index: 0.609, AUC = 0.743, 95% CI = 0.584–0.901) (Figure 3c and d).