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 m2. 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.