CXCL9 and chronic obstructive pulmonary disease: Lung function and biomarker correlations were analyzed, and unsupervised cluster analysis was used to explore inflammatory phenotypes.<h4>Results</h4>CXCL9 levels were markedly elevated in both ILD (median: 57.4 pg/mL) and COPD (70.1 pg/mL) compared to healthy smokers (32.5 pg/mL) and non-smokers (37.0 pg/mL).