Independent external validation of a nomogram to define risk categories for a significant decline in estimated glomerular filtration rate after robotic-assisted partial nephrectomy.

OBJECTIVE

To validate the Martini nomogram predicting the decline in estimated glomerular filtration rate after robotic-assisted partial nephrectomy.

METHODS

Estimated glomerular filtration rate of 406 patients from a single surgeon series was calculated before robotic-assisted partial nephrectomy and at postoperative intervals. To determine the risk group, we calculated the total score and corresponding risk of significant estimated glomerular filtration rate reduction at 15 months using the Martini nomogram. The primary outcome was a reduction in estimated glomerular filtration rate of ≥25% from preoperative levels between 1 and 12 months after surgery.

RESULTS

The median length of follow up for this study was 12 months (interquartile range 6-12 months). Overall, 134 (33%) patients were in the low-, 143 (35%) in the intermediate-, 119 (29%) in the high- and 10 (2%) in the very high-risk groups. The Kaplan-Meier estimates for the probability of significant estimated glomerular filtration rate reduction by 12 months after robotic-assisted partial nephrectomy was 12.9% in the low-risk group, 24.0% in the intermediate-risk group, 49.7% in the high-risk group and 40.0% in the very high-risk group. Harrell's C-index for discriminating between those with and without a significant reduction in estimated glomerular filtration rate 1-12 months after robotic-assisted partial nephrectomy was 0.73 (95% confidence interval 0.68-0.78).

CONCLUSIONS

The risk groups proposed by the Martini nomogram are accurate in predicting those at higher risk for a >25% decline in postoperative estimated glomerular filtration rate after robotic-assisted partial nephrectomy at 12 months.