Split Renal Function Is Fundamentally Important for Predicting Functional Recovery After Radical Nephrectomy

Abstract

While partial nephrectomy (PN) is generally preferred for localized renal cell carcinoma (RCC), radical nephrectomy (RN) is occasionally required. A new-baseline glomerular filtration rate (NBGFR) >45 ml/min/1.73 m² after kidney cancer surgery is associated with strong survival outcomes. If NBGFR after RN will be above this threshold and the tumor has increased oncologic potential, RN may be a relevant consideration. Predicting NBGFR, defined as the GFR at 3-12 mo after RN, has been challenging owing to omission of two important parameters: split renal function (SRF) and renal function compensation (RFC). Our objective was to evaluate a simple SRF-based model in comparison to five published non-SRF-based models using data from a retrospective cohort of 445 RN patients. SRF was obtained via readily available semiautomated software (FUJIFILM Medical Systems) that provides differential parenchymal volume analysis on the basis of preoperative imaging. Our conceptually simple and clinically implementable SRF-based model more accurately predicts NBGFR after RN than five published non-SRF-based models (all p < 0.01). The SRF-based model also improved prediction of the clinically relevant threshold of NBGFR >45 ml/min/1.73 m² (all p < 0.05).

Patient summary: We validated a novel approach for more accurate prediction of kidney function after removal of one kidney. Our approach can be used in clinical and practice and will help in making decisions on full or partial removal of a kidney for kidney cancer.

Keywords: Functional compensation; Kidney cancer; Parenchymal volume analysis; Radical nephrectomy; Split renal function.

Fig. 1

(A–C) Prediction of new-baseline glomerular filtration rate (NBGFR) after radical nephrectomy (RN). Renal parenchyma and tumor volumes are readily captured with parenchymal volume analysis software and shown in the top row, with the contralateral kidney (tumor-free) highlighted in (A), the ipsilateral kidney and tumor in (B), and the tumor in (C). In this hypothetical case the volume of the left kidney is 200 cm³, the volume of the right kidney plus tumor is 210 cm³, and the tumor volume is 40 cm³. The parenchymal volumes are then 200 cm³ in the left kidney and 170 cm³ in the right kidney, corresponding to a split renal function of L 54% and R 46%. If right RN is performed, the NBGFR is estimated to be (preoperative global GFR × 0.54) × 1.24. (D–I) Observed versus predicted NBGFR after RN using (D) the split renal function (SRF)-based model versus (E–I) five different published non–SRF-based models. The correlation coefficient (r) for observed versus predicted NBGFR for each model is shown. The predictive accuracy was significantly greater with the SRF-based model than with all of the non–SRF-based models (all p < 0.01). (J) Receiver operating characteristic (ROC) curves comparing the ability of the SRF-based and non–SRF-based models to discriminate postoperative NBGFR >45 ml/min/1.73 m². The area under the ROC curve (AUC) was significantly greater for the SRF-based model than for the non–SRF-based models (all p < 0.05). When the ROC curve analysis was restricted to patients with preoperative GFR >60 ml/min/1.73 m² or preoperative GFR >45 ml/min/1.73 m², entirely analogous results were obtained. CI = confidence interval.