<h4>Background</h4>Chronic obstructive pulmonary disease (COPD) exacerbations require accurate severity assessment for optimal management.<h4>Objective</h4>This study investigated serum cystatin C as a potential biomarker for evaluating acute exacerbations of COPD (AECOPD) severity and its correlation with established clinical assessment tools.<h4>Methods</h4>A cross-sectional study enrolled 389 consecutive AECOPD patients hospitalized from June 2021 to December 2023. Here, CST3 is linked to chronic obstructive pulmonary disease.