Role of cystatin C as a biomarker of acute kidney injury and as an independent long-term predictor of cardiovascular events, mortality and functional outcome

Introduction
Serum cystatin C measurements as an early biomarker of acute kidney injury (AKI) is gaining acceptance as studies confirm and define its usefulness. The aim of this study is to determine whether increase in serum cystatin C has an impact on long-term mortality, independently from the presence of the kidney injury itself.

Materials and methods
A retrospective study (20-month follow-up) was conducted in 173 not selected hospitalized patients. According to serum cystatin C concentrations, patients were stratified in risk classes by quartiles (≥0.55 and <1 mg/L; ‰¥1 and <1.17 mg/L; ‰¥1.17 and 1.57 mg/L; ‰¥1.57 and ‰¤5.29 mg/L). We compared the association of cystatin C levels with the risk for long-term mortality, after adjustment for age, sex, race and heart failure risk factors.

Results
A relationship with higher serum levels of cystatin C and mortality was found in patients with and without AKI, being stronger in patients without AKI. After multivariate adjustment, the highest quartile of cystatin C (>1.5 mg/L) was associated with a lower risk for long-term mortality. The statistical analysis (Cox regression) of the independent variables as far as mortality is concerned confirmed the significance of our result (RR 3.60; IC 1.73-7.48; p = 0.001).

Conclusions
In summary, elevated serum cystatin C level (>1.5 mg/L) was strongly and independently associated with negative clinical outcomes such as mortality and cardiovascular events, independently from the kidney injury itself. The dosage of cystatin C might play an important role in clinical practice for the assessment of cardiovascular risk stratification.