Serum cystatin C-A useful endogenous marker of renal function in intensive care unit patients at risk for or with acute renal failure?

Critically ill patients are at high risk for developing acute renal failure (ARF). The prevention of ARF is of outmost importance in order to improve the increased morbidity and mortality associated with ARF. Unfortunately, there is lack of adequate endogenous markers that can identify renal dysfunction early - this hampers timely application of measures to prevent further renal damage. The use of exogenous markers of renal function is not only time-consuming but also expensive, and therefore can not be used on a regular basis in the intensive care unit. Both the presently used endogenous and exogenous markers are not reliable during continuous renal replacement therapy (CRRT) because these markers are removed by the therapy itself impeding early detection of recovering of renal function. Cystatin C has been proposed as an alternative endogenous marker of renal function for more than 15 years. In this manuscript we review the literature on the role of cystatin C as marker for renal function, focusing on the critically ill patient. Serum cystatin C concentrations have been found to relate to renal impairment and suggest that cystatin C is more sensitive to detect mild decreases in GFR. Cystatin C could be an important tool both to recognize early renal dysfunction and to identify renal recovery while on CRRT in the critically ill patient, however, we are in need of more studies.