The inaccuracy of cystatin C and creatinine-based equations in predicting GFR in orthotopic liver transplant recipients.

BACKGROUND As survival with an orthotopic liver transplant (OLT) improves, the incidence of chronic kidney disease in OLT recipients increases. Measurement of kidney function using creatinine-based estimates is often inaccurate, while cystatin C may overcome the biases that effect creatinine. The aim of this study was to assess the accuracy of creatinine- and cystatin C-based equations to estimate kidney function in long-term OLT recipients. METHODS This was a cross-sectional study performed on OLT recipients within a single liver transplant centre where creatinine (n = 41) and cystatin C (n = 30) were measured and glomerular filtration rate (GFR) estimated using the Modification of Diet and Renal Disease (MDRD), Cockcroft-Gault (CG), Hoek, Larsson, Filler and Le Bricon equations. Comparison was made with the nuclear GFR (nGFR) (n = 41) measured through 51-Cr EDTA clearance. RESULTS The mean age of recipients was 56 +/- 13 years, and they were 6.5 +/- 4.7 years post-OLT. Fifty-six percent of recipients had a nGFR < or =60 mL/min/1.73 m(2). nGFR correlated significantly with all predictive equations (P < 0.001). The MDRD, CG and Le Bricon equations had the smallest degree of bias (-7.6, -7.3 and 3.4 mL/min/1.73 m(2), respectively), with 22%, 22% and 27% of estimates, respectively, being within 10% of nGFR measurements. In OLT recipients with nGFR < or =60 mL/min/1.73 m(2), the degree of bias of both the creatinine-base MDRD and cystatin-based Hoek equations was within 2 mL/min/1.73 m(2) difference between the measured and estimated GFR, but 41% and 36% of estimates were within 10% of the nGFR measurement. CONCLUSIONS Therefore, the degree of inaccuracy in cystatin C- and creatinine-based predictive equations brings into question their clinical utility in OLT recipients. We have no evidence that cystatin C is superior to creatinine in this population.