Utility of serum cystatin C measured at diagnosis in evaluating cross-sectional activity and predicting all-cause mortality in patients with antineutrophil cytoplasmic antibody-associated vasculitis.

INTRODUCTION/

objectivesWe investigated the utility of serum cystatin C (CysC) at diagnosis in evaluating cross-sectional activity and predicting all-cause mortality (ACM) during follow-up in patients with antineutrophil cytoplasmic antibody-associated vasculitis (AAV).

methodsWe retrospectively reviewed the medical records of 323 patients with AAV enrolled in a single-centre cohort of Korean patients and included 109 patients meeting the inclusion criteria. The Birmingham Vasculitis Activity Score (BVAS) and Five-Factor Score (FFS) were used for assessing AAV activity and anticipating prognosis. ACM alongside end-stage kidney disease during follow-up were investigated as poor outcomes.

resultsThe median age of the 109 patients was 66.0 years, with 45.0% being male. Among them, 77, 17, and 15 had MPA, GPA, and EGPA, respectively. Serum CysC at diagnosis exhibited a significant positive correlation with cross-sectional BVAS, alongside age and FFS. When the cut-off of serum CysC for ACM was set at 2.56 mg/L, patients with serum CysC ≥ 2.56 mg/L at diagnosis had a significantly higher relative risk of ACM during follow-up than those without (10.988). Patients with serum CysC ≥ 2.56 mg/L at diagnosis exhibited a significantly lower cumulative survival rate compared to those without. In multivariable Cox proportional analysis, serum CysC ≥ 2.56 mg/L at diagnosis (hazard ratio 5.994) remained independently associated with ACM during follow-up alongside male sex and BVAS at diagnosis. By contrast, serum creatinine was not significantly associated with ACM, suggesting that CysC may provide incremental prognostic value beyond conventional renal indices.

conclusionThis study is the first to demonstrate the potential clinical utility of serum CysC at diagnosis in assessing cross-sectional disease activity and predicting ACM during follow-up in AAV patients independently of baseline kidney function. These findings are preliminary and should be validated in larger prospective cohorts. Key Points • Serum cystatin C measured at diagnosis was significantly associated with disease activity in antineutrophil cytoplasmic antibody-associated vasculitis (AAV). • Cystatin C levels reflected systemic inflammation beyond the effect of baseline renal function. • A cystatin C level ≥2.56 mg/L independently predicted all-cause mortality during follow-up. • This study is the first to demonstrate the prognostic value of serum cystatin C in patients with AAV.