Elevated serum cystatin C predicts tophus formation in gout: evidence from a cross-sectional study

To investigate the association between serum cystatin C (CysC) levels and tophus presence, and to assess its diagnostic value for structural joint damage in gout.

In this cross-sectional study of 598 gout patients, we examined the association between serum CysC and both the presence and burden of tophi. The predictive value of CysC for tophus and bone erosion was further evaluated using logistic regression and ROC curve analyses.

Elevated serum CysC levels were significantly associated with older age, longer disease duration, and an increased prevalence of tophus, bone erosion, and the patients in the highest quartile (Q4, >1.28 mg/L) had a 3.87-fold higher adjusted odds of tophus (P < 0.05), showing a significant dose-response trend (P for trend = 0.003). Serum CysC alone demonstrated a moderate predictive value for tophus (AUC = 0.627), which improved in multivariable models (AUC = 0.777). A similar enhancement in predictive performance was noted for bone erosion (fully adjusted AUC, 0.756). There was a significant interaction between serum CysC and magnesium regarding tophus risk (P < 0.001). Furthermore, multivariate ordinal regression analysis identified higher CysC, longer gout duration, bone erosion, and the double contour sign as independent predictors of tophus burden.

Serum CysC independently predicts tophus in gout and shows interaction with serum magnesium. Its integration into risk assessment may improve clinical stratification and support timely, individualized treatment strategies.