Prediction of GFR in liver transplant candidates

Abstract

Background: Kidney function frequently is impaired in patients with cirrhosis; however, glomerular filtration rate (GFR) is difficult to estimate in these patients by using standard clinical markers. The aim of our study is to compare GFR calculated from renal clearance of iodine 125-labeled iothalamate (125I-iothalamate) with the plasma decay technique and the Modification of Diet in Renal Disease (MDRD) and Cockroft-Gault (CG) prediction equations. Methods: We performed a cross-sectional study of patients with liver cirrhosis being evaluated for transplantation (50% Child's class C); 89% had ascites or edema and 44% were men aged 55 ± 2 years. Average pretest blood urea nitrogen level was 16 ± 2 mg/dL (5.7 ± 0.7 mmol/L); serum creatinine, 1.0 ± 0.1 mg/dL (88 ± 9 μmol/L; range, 0.6 to 1.7 mg/dL [53 to 150 μmol/L]); plasma albumin, 3.14 ± 0.16 g/dL (31.4 ± 1.6 g/L); and total bilirubin, 4.0 ± 0.7 mg/dL (67 ± 11.3 μmol/L). Kidney function was measured by means of simultaneous plasma and renal clearance of 125I-iothalamate (Glofil-125; Cypros Pharmaceutical Corp, Carlsbad, CA) and the MDRD and CG equations. Results: GFRs were 58.2 ± 5.1 mL/min/1.73 m2 by renal clearance of 125I-iothalamate and 76.7 ± 7.2 mL/min/1.73 m2 by the plasma decay technique (+18.5 mL/min, or 32%; P = 0.0004). GFR by the MDRD equation was 76.9 ± 7.8 mL/min/1.73 m2 (+18.7 mL/min, or 32%; P = 0.0004 versus renal iothalamate; r2 = 0.57). GFR by the CG equation was the least accurate (+30.1 mL/min, or 52%; P = 0.0001 versus renal iothalamate). Conclusion: The current clinically used CG and MDRD equations to estimate kidney function in patients with cirrhosis and volume excess and the 125I-iothalamate plasma decay technique are inaccurate because they overestimate GFR. It seems very unlikely that accurate and reliable formulas will be developed that are able to replace the formal measurement of GFR in patients with liver cirrhosis. Therefore, we conclude that despite the additional complexity, renal clearance techniques should be used to assess GFR accurately in patients with liver cirrhosis and ascites.