The area under the curve (AUC) showed that only plasma YKL-40 could distinguish patients with features of ACO from COPD patients (ROC AUC = 0.7138), and only NGAL was useful in distinguishing patients with features of ACO from asthma patients (ROC AUC =0.7517). This evidence concerns the gene CHI3L1 and chronic obstructive pulmonary disease.