C-Index is Associated With Functional Outcomes After Laparoscopic Partial Nephrectomy

Purpose: The C-index is a morphometric descriptor of renal masses that incorporates tumor size and site. We examined associations of the C-index with kidney function after laparoscopic partial nephrectomy. Materials and Methods: We retrospectively reviewed the records of 131 patients who underwent laparoscopic partial nephrectomy for a single kidney tumor. We calculated the C-index from preoperative contrast enhanced computerized tomography images. Estimated glomerular filtration rate was calculated using the modification of diet in renal disease 2 equation. Nadir estimated glomerular filtration rate was calculated using peak serum creatinine within 7 days of surgery. Results: The median C-index was 2.7 (range 0.7 to 9.6). The median preoperative and nadir estimated glomerular filtration rate was 78 (range 23 to 148) and 54 ml/minute/1.73 m(2) (range 15 to 127, p <0.001). The mean +/- SD total glomerular filtration rate decrease was 28% +/- 16%. On univariate analysis we noted a positive correlation between log C-index and the nadir estimated glomerular filtration rate (r = 0.29, p = 0.002), and a negative correlation between log C-index and the percent decrease in the estimated glomerular filtration rate (r = -0.4, p <0.001). On multivariate analysis the estimated glomerular filtration rate percent decrease was significantly associated with log C-index (p = 0.005) and warm ischemia time (p <0.001) but not with tumor diameter or the preoperative estimated glomerular filtration rate. Of patients with a C-index of 2.5 or less 70% showed a 30% or greater decrease in the estimated glomerular filtration rate vs 32% of those with a C-index of greater than 2.5 (RR 2.2, p <0.001). Conclusions: The C-index is associated with the postoperative nadir estimated glomerular filtration rate and the percent decrease in the estimated glomerular filtration rate after laparoscopic partial nephrectomy. A C-index of less than 2.5 correlated with a 2.2-fold increased risk of a 30% or greater estimated glomerular filtration rate decrease after laparoscopic partial nephrectomy.