725 POST-OPERATIVE RENAL FUNCTION AFTER NEPHRECTOMY: HOW MUCH DOES THE REMAINING KIDNEY COMPENSATE

Abstract

INTRODUCTION AND OBJECTIVES: Pre-operative renal scan calculates differential function of the non-removed kidney. Along with pre-operative eGFR, we should be able to accurately calculate an expected postoperative eGFR based on percentage GFR removed by nephrectomy as determined by renal scan. However, observed postoperative GFR is often different than expected due to compensatory response of the remaining kidney. In this study, we measure the actual ability of the remaining kidney to compensate after nephrectomy. METHODS: We conducted a retrospective review of 108 patients who underwent nephrectomy or nephroureterectomy at a single institution between 2001-2011, who had a pre-operative renal scan with calculated differential function. GFR values preand post-operatively were calculated with the MDRD equation. Expected post-operative GFR was compared to actual GFR. Demographic information which led to differences in expected vs. observed GFR were analyzed including co-morbidities, rationale for surgery, and final pathology. RESULTS: The average age of patients undergoing surgery was 56.1 (SD 13.8) years, and the reason for nephrectomy or nephroureterectomy was for benign causes in 45 cases and malignant causes in 63 cases. The average preoperative creatinine and calculated GFR (cGFR) were 1.0 (SD 0.2) mg/dL and 72.7 (SD 25.7) mL/min/1.73 m2, The average postoperative creatinine and cGFR were 1.4 (SD 0.6) mg/dL and 54.6 (SD 22.8) mL/min/1.73 m2. Observed postoperative GFR exceeded the expected GFR by 14.7%. When stratified by preoperative GFR, the observed GFR exceeded the expected GFR by 6.0%, 11.5%, and 23.4% for those with GFR’s 90, between 90 and 60, and 60 mL/min/1.73 m2 respectively (p 0.020). When accounting for various patient factors such as age, race, gender, diabetes, hypertension, hyperlipidemia, coronary artery disease, nephrolithiasis, smoking history and BMI; only female gender (LR 4.57, p 0.040) predicted poorer renal function than expected. CONCLUSIONS: After nephrectomy, the remaining kidney exceeded expected post-operative GFR by 15% in this cohort of patients with pre-operative renal scans. Patients with existing renal insuffiency had the greatest compensatory response. This information can provide valuable information to clinicians and patients about expected renal recovery.