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 creatininebased methods is potentially inaccurate in patients with cirrhosis. Cirrhotic patients have several underlying conditions that contribute to falsely low serum creatinine concentrations, even in the presence of moderate to severe renal impairment. Therefore creatinine-based methods usually overestimate true GFR in these patients. Cystatin-C is a low molecular weight protein and an endogenous marker of GFR. We compared the accuracy of plasma cystatin-C and creatinine in assessing renal function in cirrhotic patients. METHODS We serially enrolled cirrhotic patients with stable renal function admitted in our ward if they met the inclusion criteria and consented to participate. Child- Pugh (CP) score was calculated for all patients. GFR was calculated using serum creatinine, serum cystatin-C, and 99m TC-DTPA clearance with the last one serving as the gold standard. The area under curve (AUC) on receiveroperating characteristic curves (ROC) were used to assess the diagnostic accuracy of 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 predicting the true GFR, while serum creatinine performed relatively accurately at GFR<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-C could not predict GFR effectively even after stratification for CP score, gender, and BMI. Serum creatinine could predict GFR<65ml/min in females (ROC curve AUC=0.844, p=0.045). In those with BMI>20 kg/m2 a GFR<80 ml/min could 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 curve AUC=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 cirrhotic patients, although serum creatinine seems to perform better in selected subgroups.