CHI3L1 and chronic obstructive pulmonary disease: The AUC of the ROC analysis for differentiating ACO (COPD) from COPD was significantly higher in serum EDN than in serum periostin or YKL-40, with a cut-off value of 22.4 ng/mL, a sensitivity of 86.2%, a specificity of 55.7%, and an AUC of 0.75 (95% CI, 0.64–0.85; p = 0.002) (Figure 3).