Clinical significance of cystatin C in acute coronary syndromes: something more than a marker of renal function?

Serum cystatin C (Cys-C) levels perform better than other markers of renal function as indicator of cardiovascular outcome both in population-based studies and in patients with non-ST-elevation acute coronary syndrome (NSTE-ACS). Whether the relation between elevated serum Cys-C levels and risk of a worse cardiovascular prognosis reflects a more precise measurement of renal function or an association with non-renal factors such as inflammation is a matter still poorly defined. In a prospective, multicenter study our group evaluated the time course of serum Cys-C levels in 222 patients over the first 6 weeks after an episode of NSTE-ACS and a successful percutaneous revascularization. We observed that Cys-C levels slightly but significantly increased from the admission to 6-week samples (7.1 to 7.8 mg/dL, p <0.0001), contrary to high sensitivity C Reactive Protein (hsCRP), N-terminal portion of the proBNP peptide (NT-proBNP), and Interleukin 6 (IL-6) levels which significantly decreased in the same period. Cys-C levels were not different in patients with or without elevated troponin (c-TnT), whereas the other inflammatory and biomechanical markers showed higher values in patients with versus those without elevated c-TnT. Cys-C was highly correlated with estimated glomerular filtration rate both in ACS and 6-week samples. In conclusion, our data seem to contradict the hypothesis that inflammation is a determinant of the Cys-C levels because they did not show the typical pattern of an acute-phase reactant and secondly they were independent from myocardial necrosis diagnosed by c-TnT levels. Moreover, our results indicate that Cys-C remains a reliable marker of renal function also during ACS because is not affected by myocardial necrosis or by acute left ventricular impairment, as detected by increased NT-proBNP values