Serum Cystatin C as a Marker of Renal Function in Critically Ill Patients With Normal Serum Creatinine

BACKGROUND Serum creatinine as a classic marker of renal function has several limitations in the detection of renal dysfunction. OBJECTIVES This study assessed the validity of serum cystatin C as a marker of renal function in critically ill patients with normal serum creatinine. PATIENTS AND METHODS Eighty adult patients referred to intensive care units with serum creatinine levels < 1.5 mg/dL and without hemodynamic instability were chosen and their serum creatinine and cystatin C levels were measured. A 24-hour urine sample was collected to calculate creatinine clearance (Ccr). Renal dysfunction was defined as Ccr < 80 mL/min/1.73 m(2). RESULTS There were significant correlations between measured Ccr and 1/serum creatinine (R = 0.51, P < 0.001) and 1/serum cystatin C (R = 0.25, P = 0.028). The difference between false negative rates of serum creatinine (93.33%) and cystatin C (80%) in the detection of renal dysfunction was significant (P = 0.032). Receiver operating characteristic curve analysis illustrated that area under the curve of serum creatinine and cystatin C for detecting renal dysfunction were 0.711 and 0.607, respectively; however, this difference was not significant (P = 0.222). CONCLUSIONS Our data demonstrated that serum cystatin C is not superior to serum creatinine in the early detection of renal dysfunction in critically ill patients.