CHI3L1 and chronic obstructive pulmonary disease: Recently, serum EDN was found to be higher in ACO patients than that in asthma or COPD patients and had the highest specificity (82.4%) when combined with high serum YKL-40 levels based on cutoff values derived by receiver operating characteristics analysis (EDN: 23.0 ng/mL; YKL-40: 61.3 ng/mL) [39].