Pöge U et al. (2006) Calculation of glomerular filtration rate based on cystatin C in cirrhotic patients. Nephrol Dial Transplant 21: 660–664

Using serum creatinine or creatinine clearance values overestimates glomerular filtration rate (GFR) in patients with liver cirrhosis. Cystatin C has previously been shown to be more precise than creatinine in GFR monitoring and could therefore be a better marker of renal function in these patients. Pöge et al. compared the accuracy of the Hoek and Larsson cystatin-C-based formulas in predicting GFR with the accuracy of the creatinine-based Modification of Diet in Renal Disease and Cockcroft–Gault equations; all four equations were developed using data from patients without liver cirrhosis.

In this retrospective analysis of 44 cirrhotic patients (30 male, median age 52.9 years), serum creatinine and cystatin C were measured and GFR was calculated using each of the four equations. Compared with the true GFR (determined using the inulin clearance technique), all equations overestimated GFR, with median overestimations ranging from 105% to 154% (P <0.0001). Precision was better, and bias was less, for rates estimated using the cystatin-C-based equations than for GFR estimated using the creatinine-based equations. Correlation with inulin clearance and accuracy were slightly better with the cystatin-C-based formulas than with either of the creatinine-based equations.

So, estimates of GFR based on cystatin C are superior to those based on creatinine, but still overestimate GFR in patients with liver disease. As such, the authors recommend that inulin clearance be used to assess renal function until more-reliable formulas can be developed using data from cirrhotic patients. Basing these equations on a serum parameter such as cystatin C will preclude the introduction of inaccuracies due to errors in urine collection.