Cystatin C Provides More Information Than Other Renal Function Parameters for Stratifying Risk in Patients With Acute Coronary Syndrome

Introduction and objectives. The protein cystatin C has a stable plasma concentration and is eliminated exclusively by the kidneys. The aim of this study was to determine the prognostic value of cystatin C in patients with acute coronary syndrome (ACS). Methods. The prospective study included 203 hospitalized ACS patients. Clinical evaluation during the first 24 hours of hospitalization included a hemogram and measurement of creatinine, cystatin C, total and fractionated cholesterol and markers of myocardial necrosis. The glomerular filtration rate (GFR) was estimated using the MDRD (Modification of Diet in Renal Disease) equation. A comparison was made between two groups of patients divided according to a serum cystatin-C level above or below 0.95 mg/L. The mean follow-up period was 151 days. Results. In total, 90 patients (44.3%) had a cystatin-C level <= 0.95 mg/L and 113 (55.7%) had a level >0.95 mg/L. Those with a cystatin-C level >0.95 mg/L had poorer in-hospital outcomes, including more frequent heart failure (51.3% vs. 13.3%; P=.001) and higher in-hospital mortality (17.6% vs. 3.3%; P=.001), as well as higher mortality throughout follow-up (22.0% vs. 5.6%; P=.001). Multivariate analysis adjusted for age, ejection fraction and troponin-I and high-sensitivity C-reactive protein concentrations showed that cystatin C was the most powerful independent predictor of a cardiovascular event (relative risk=1.91; 95% confidence interval, 1.03-3.53). Patients with a GFR >60 mL/1.73 m(2) and a cystatin-C level >0.95 mg/L had higher in-hospital mortality (10.2% vs. 3.9%; P=.001). Conclusions. Measurement of cystatin C in high-risk ACS patients may be clinically useful for risk stratification during hospitalization, particularly in those with a normal GFR.