STOCKHOLM, SWEDEN (UroToday.com) - Following radical cystectomy and urinary diversion, estimated glomerular filtration rate (eGFR) is routinely used to monitor renal function.
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Actual GFR, however, as measured by 99MTc-DTPA (iGFR), is more accurate but not routinely measured at most institutions. The authors report the accuracy of eGFR compared to iGFR measurements and long-term trends in renal function following cystectomy and urinary diversion. eGFR and iGFR were identified and compared among 166 patients following cystectomy.
In total, 614 paired iGFR and eGFR results were analyzed. A significant linear correlation between iGFR and eGFR was observed (r=0.792, p < 0.0001). The iGFR:eGFR ratio correlated inversely with increasing age (r=-0.42, p < 0.0001). Overall, better renal function was associated with a higher level of underestimation by eGFR. Of 85 patients with at least 5 years follow-up and multiple iGFR measurements, 79.8% experienced an overall decline of at least 1% of baseline function (92.9% overall decline). In 22.4% of these 85 patients, a decline of at least 10% in iGFR occurred and was missed by eGFR measurements, which overestimated true renal function. 65.6% of total overestimations occurred in patients with an iGFR range between 45 and 89 mls/min/1.73m2. Correlation between renal function and level of overestimation by eGFR was not statistically significant (r=0.00049, p=0.9368).
In conclusion, eGFR is more likely to underestimate true renal function in younger patients, and greater underestimations occur as iGFR increases. Overestimations are more common in clinically relevant ranges, and significant loss in older patients can still occur, undetected, if eGFR is used in isolation. In order to detect early signs of nephron damage, the authors recommend serial iGFR measurement for a short period following cystectomy and ileal loop diversion.
Presented by C. D. Tait at the 29th Annual European Association of Urology (EAU) Congress - April 11 - 15, 2014 - Stockholmsmässan - Stockholm, Sweden.
Salford Royal NHS Foundation Trust, Department of Urology, Salford UK
Written by Jeffrey J. Tomaszewski, MD, medical writer for UroToday.com