Estimation of glomerular filtration rates after orthotopic liver transplantation:: Evaluation of cystatin C-based equations

Early detection of renal dysfunction in patients after orthotopic liver transplantation is important. Creatinine-based equations to estimate glomerular filtration rate (GFR) were found to be less accurate in liver transplant recipients than in their original populations. Since cystatin C (CysC) is independent from muscle mass and hepatic biosynthesis, we evaluated the diagnostic accuracy of 3 CysC-based equations (Larson, Hoek, and Filler formulae) that are based on the same CysC method as that of our center in comparison to the abbreviated creatinine-based modification of diet in renal disease (MDRD) formula in 59 liver transplant recipients. "True GFR" was measured by 99mTc-diethylene triamine pentaacetic acid (Tc-99m-DTPA) clearance. Neither correlation with the GFR (correlation coefficients: 0.594-0.640) nor precision (root mean square error: 15.7-18.17 mL/min/1.73 m(2)) differed significantly between the tested formulae. The biases of the Hoek and Larsson formulae were significantly smaller than those of the MDRD and Filler equations (-0.1 and -2.3 vs. 10.1 and 7.9 mL/min/1.73 m(2), respectively; P <= 0.0023). Mean estimates of MDRD (61.9 +/- 21.4 mL/min/1.73 m(2)) and Filler (61.2 +/- 22.1 mL/min/1.73 m(2)) differed significantly from the measured GFR (52.3 +/- 17.5 mL/min/1.73 m(2); P < 0.005), whereas Larsson and Hoek did not (49.5 +/- 20.2 and 51.4 +/- 17.9 mL/min/1.73 m(2), respectively). Accuracy within 30% and 50% of the true GFR was best for the Hoek (76.3% and 93.2%) formula, albeit not significantly different from MDRD (64.4% and 83.1%). Taken together, these data show the best overall performance for GFR estimates derived from the Hoek equation with respect to bias, precision, and accuracy.