Estimated glomerular filtration rate is unreliable in detecting renal function loss during follow-up after cystectomy and urinary diversion.

PURPOSE: To evaluate the accuracy of estimated glomerular filtration rate (eGFR) against the reference standard of isotopic GFR (iGFR) in monitoring renal function during follow-up after cystectomy and urinary diversion.
METHODS: Patients who had undergone cystectomy and ileal conduit urinary diversion at two centres between August 2001 and August 2006 were identified. eGFR calculated using the MDRD formula was compared to (51)Cr EDTA measured iGFR values measured at similar time-points during follow-up.
RESULTS: Six hundred and fourteen paired iGFR and eGFR results were analysed from 166 patients (18% female, median age 70 years). There was a significant difference between paired iGFR and eGFR measurements (p < 0.0001) with a mean bias of +1.8 mls/min/1.73 m(2) (SD 18.0) and a 95% limit of agreement of -33.5 to 37.2 mls/min/1.73 m(2). iGFR and eGFR values converged at a GFR of approximately 45 mls/min/1.73 m(2). 70.6% of patients experienced a loss of renal function greater than expected (>0.58 mls/min/1.73 m(2)/year). In 22.4% of these patients, a decline of greater than 10% in iGFR occurred that was undetected by eGFR measurements, which overestimated GFR. There was no significant relationship between patient height, weight or body mass index and the accuracy of eGFR measurements.
CONCLUSIONS: iGFR measurement is recommended following ileal conduit urinary diversion if early signs of renal function loss are to be detected. eGFR overestimates GFR in critically relevant ranges and fails to detect loss in a clinically significant proportion of patients.