Serum cystatin C measurement in differential diagnosis of intra and extrahepatic cholestatic diseases.

OBJECTIVE Cystatin C is a very potent inhibitor of cysteine proteinases and, it has been clinically applied as a sensitive marker in monitoring of renal and liver functions. The aim of this study was to reveal whether cystatin C may be a useful marker for distinguishing intra- versus extrahepatic cholestasis. MATERIALS AND METHODS Serum cystatin C concentrations were determined by nephelometric immunoassay using N latex cystatin C kit in 53 patients with cholestatic disorder that included 18 patients with intrahepatic cholestasis , 17 patients with malignant extrahepatic cholestasis , 18 patients with benign extrahepatic cholestasis. Serum cystatin C concentration was also determined in 20 healthy volunteers. RESULTS Mean serum cystatin C concentration was 2.82 +/- 0.24 mg/l (SD) in patients with intrahepatic cholestasis, 2.05 +/- 0.15 mg/l in patients with extrahepatic malignant cholestasis, 1.37 +/- 0.13 mg/l in extrahepatic benign cholestatic patients and 0.93 +/- 0.24 mg/l in control group. Serum cystatin C concentrations in patients with cholestatic disease were significantly higher than those in the healthy controls (p < 0.001). Moreover, mean serum cystatin C concentration in patients with intrahepatic cholestasis was higher than those in extrahepatic cholestasis groups (p < 0.001). Serum cystatin C concentrations were significantly higher in patients with malignant xtrahepatic cholestasis than in patients with benign extrahepatic cholestasis p < 0.001). There were no correlations patients among serum cystatin C concentrations and serum levels of AST, ALT, ALP, GGT, total and conjugated bilirubin. CONCLUSION Our results suggested that serum cystatin C level may be a potential biochemical marker both to point out an intrahepatic origin by excluding an extrahepatic source of cholestasis in patients with jaundice and to possibly differentiate bening and malignant extrahepatic cholestatic disorders.