Comparison of 99mTc-DTPA plasma clearance and estimated glomerular filtration rate in the renal hypothermia trial
Francis Lemire1, Dean A. Fergusson2, Greg Knoll2,3, Christopher Morash1, Luke T. Lavallée1,2, Ranjeeta Mallick2, Antonio Finelli4, Anil Kapoor5, Frédéric Pouliot6, Jonathan Izawa7, Ricardo A. Rendon8, Ilias Cagiannos1, Rodney H. Breau1,2.
1Division of Urology, Department of Surgery, The Ottawa Hospital, University of Ottawa, Ottawa, ON, Canada; 2Clinical Epidemiology Program, Ottawa Hospital Research Institute, University of Ottawa, Ottawa, ON, Canada; 3Division of Nephrology, Department of Medicine, The Ottawa Hospital, University of Ottawa, Ottawa, ON, Canada; 4Division of Urology, Departments of Surgery and Surgical Oncology, Princess Margaret Cancer Centre, University Health Network and University of Toronto, Toronto, ON, Canada; 5Division of Urology, Department of Surgery, McMaster University, Hamilton, ON, Canada; 6Division d'Uologie, Département de Chirurgie, Université Laval, Québec, QC, Canada; 7Division of Urology, Department of Surgery, Western University, London, ON, Canada; 8Division of Urology, Department of Surgery, Dalhousie University, Halifax, NS, Canada
Introduction: The gold standard test to measure glomerular filtration rate (GFR) is a 99mTc-DTPA plasma clearance renal scan, however, these tests are cumbersome for patients and expensive compared to GFR estimation using serum creatinine concentrations. In this study, we aimed to compare measured GFR based on 99mTc-DTPA plasma clearance (mGFR) and estimated GFR using the CKD-EPI equation (eGFR) in order to assess the need for expensive renal scans in surgical urology trials.
Methods: We performed a post-hoc analysis of the randomized controlled renal hypothermia trial. This trial was conducted at five Canadian academic centers and showed no benefit of renal hypothermia during open partial nephrectomy. Renal function was assessed preoperatively and one-year postoperatively using the 99mTc-DTPA plasma clearance (mGFR) and using the CKD-EPI creatinine equation (eGFR). Statistical comparison of mGFR and eGFR was performed and interpreted using Pearson correlation coefficient. Subgroup analyses were performed according to baseline kidney function, age, patient sex, and ethnicity. Differences between mGFR and eGFR were categorized as small (less than 10 ml/minute/1.73 m2) moderate (10–20 ml/minute/1.73 m2), and large (>20 ml/minute/1.73 m2).
Results: Overall, the comparison of 341 mGFR and eGFR assessments demonstrated a strong correlation (0.81, p<0.0001). Subgroups analyses based on kidney function, age, sex, and ethnicity remained highly correlated. One hundred ninety-two (56%) patients had small differences between mGFR and eGFR, 98 (28.7%) had moderate differences, and 52 (15.3%) had large differences.
Conclusions: This study showed that eGFR using serum creatinine is adequate in partial nephrectomy clinical trials and expensive assessments of plasma clearance are unnecessary. This information should improve the feasibility of future partial nephrectomy clinical trials without compromising validity.
