Feasibility of cystatin C as a biomarker for AECOPD severity: a cross-sectional study integrating CAT score, mMRC grade, and GOLD stage.

Background: Chronic obstructive pulmonary disease (COPD) exacerbations require accurate severity assessment for optimal management. Objective: 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. Methods: A cross-sectional study enrolled 389 consecutive AECOPD patients hospitalized from June 2021 to December 2023. Patient demographics, laboratory parameters, arterial blood gases, CAT scores, mMRC grading, and GOLD staging were collected. Statistical analyses included Spearman correlation, ANOVA, multiple regression, ROC curve analysis, and restricted cubic spline modeling. Results: Patients averaged 68.71 ± 0.8 years with 71.7% male pre-dominance. Cystatin C levels progressively increased across CAT score severity groups: mild (< 10 points) 1.080 ± 0.32 mg/L, moderate (10-20) 1.380 ± 0.41 mg/L, severe (21-30) 1.720 ± 0.52 mg/L, and very severe (>30) 2.150 ± 0.68 mg/L ( Conclusion: Serum cystatin C strongly correlates with AECOPD severity across multiple assessment scales and demonstrates good diagnostic accuracy, supporting its potential as a reliable biomarker for clinical severity evaluation in COPD exacerbations.