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 ( F = 78.42, P 0.001). Strong positive correlations existed between cystatin C and CAT scores ( rs = 0.687), mMRC grading ( rs = 0.612), and GOLD staging ( rs = 0.534, all P 0.001). Multiple regression confirmed cystatin C as an independent CAT score predictor (β = 5.89, 95%CI: 4.72–7.06, P 0.001). For severe AECOPD prediction (CAT ≥ 21), cystatin C demonstrated good diagnostic performance with AUC 0.847 (95%CI: 0.807–0.887), optimal cutoff 1.52 mg/L, sensitivity 81.5%, and specificity 78.2%. Restricted cubic spline analysis revealed a significant non-linear dose-response relationship ( P = 0.023). 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.