Serum cystatin-C is not superior to serum creatinine in predicting glomerular filtration rate in cirrhotic patients.

Background: Assessment of glomerular filtration rate (GFR) by common creatininebasedmethods is potentially inaccurate in patients with cirrhosis. Cirrhoticpatients have several underlying conditions that contribute to falsely low serumcreatinine concentrations, even in the presence of moderate to severe renalimpairment. Therefore creatinine-based methods usually overestimate trueGFR in these patients. Cystatin-C is a low molecular weight protein and anendogenous marker of GFR. We compared the accuracy of plasma cystatin-Cand creatinine in assessing renal function in cirrhotic patients.
Methods: We serially enrolled cirrhotic patients with stable renal function admitted inour ward if they met the inclusion criteria and consented to participate. Child-Pugh (CP) score was calculated for all patients. GFR was calculated usingserum creatinine, serum cystatin-C, and 99m TC-DTPA clearance with the lastone serving as the gold standard. The area under curve (AUC) on receiveroperatingcharacteristic curves (ROC) were used to assess the diagnostic accuracyof each calculated GFR with that measured by DTPA.
Results: Fourty-eight patients were enrolled (32 males, 66.7%). Nine were in class-A,20 in class-B and 19 in class-C of CP. Cystatin-C did not perform well in predictingthe true GFR, while serum creatinine performed relatively accurately atGFR<80ml/min (AUC=0.764, p=0.004). Serum creatinine at a cutoff of 1.4 mg/dl was 20% sensitive & 92% specific and with at a cutoff of 0.9 mg/dl was 77%sensitive & 72% specific for diagnosis of impaired renal function. Cystatin-Ccould not predict GFR effectively even after stratification for CP score, gender,and BMI. Serum creatinine could predict GFR<65ml/min in females (ROCcurve AUC=0.844, p=0.045). In those with BMI>20 kg/m2 a GFR<80 ml/mincould also be predicted by serum creatinine (ROC curve AUC=0.739, p=0.034).It also could predict GFR<80ml/min in patients with CP class A & B (ROC curveAUC=0.795, p=0.01), but not in patients with CP class C.
Conclusion: Neither serum creatinine nor Cystatin-C are good predictors of GFR in cirrhoticpatients, although serum creatinine seems to perform better in selectedsubgroups.