Validation of new baseline renal function predictive model in robotic-assisted partial nephrectomy cohort

To validate a new baseline estimated glomerular filtration rate (NB-GFR) formula in a cohort of robotic-assisted partial nephrectomies (RAPN).

NB-GFR = 35 + preoperative GFR (× 0.65) - 18 (if radical nephrectomy) - age (× 0.25) + 3 (if tumor size >7 cm) - 2 (if diabetes). NB-GFR was calculated in 464 consecutive RAPN from a single surgeon cohort. 143 patients were excluded secondary to insufficient eGFR follow up. We analyzed NB-GFR accuracy utilizing the last observed eGFR 3-12 months post RAPN. Categorical variables were summarized with the frequency and percentage of patients. Numerical variables were summarized with the median, 25^th percentile, and 75^th percentile.

The mean difference between observed and predicted NB-GFR was 4.6 ml/min/1.73m² (95% CI -6.9 to 16.1 ml/min/1.73m² ). There was a pattern of higher observed NB-GFRs being underestimated by the NB-GFR equation while lower observed NB-GFRs were overestimated by the NB-GFR equation. The NB-GFR formula had a high level of accuracy with 98.8% of predicted NB-GFRs falling within 30% of the observed NB-GFR (95% CI 86.8% to 99.5%). The median and interquartile range of the difference between observed and predicted NB-GFR was 3.9 ml/min/1.73m² (IQR 0.7 to 8.2 ml/min/1.73m² ). The sensitivity, specificity, positive predictive value, and negative predictive value for the ability of predicted NB-GFR to identify those with an observed NB-GFR <60 ml/min/1.73m² after RAPN was 98%, 92%, 88%, and 99%, respectively.

The NB-GFR equation developed with partial and radical nephrectomy cohorts is accurate in predicting post-operative eGFR 3-12 months following RAPN.