Preoperative nuclear renal scan underestimates renal function after radical nephrectomy

Objective To compare expected and actual renal function after nephrectomy. Nuclear renal scan estimates differential kidney function and is commonly used to calculate expected postoperative renal function after radical nephrectomy. However, the observed postoperative renal function is often different from the expected. Methods A retrospective review was performed on 136 patients who underwent radical nephrectomy or nephroureterectomy and had a preoperative renal scan with calculated differential function. Results Glomerular filtration rate (GFR) values, preoperative and postoperative, were calculated with the Modification of Diet in Renal Disease (MDRD) equation. The expected postoperative GFR based on renal scan was compared with the actual postoperative GFR. The average age of patients undergoing surgery was 58.6 years, and the indication for surgery was for benign causes in 59 (44%) patients and cancer in 76 (56%) patients. The average preoperative creatinine and estimated GFR were 1.0 mg/dL and 69.9 mL/min/1.73 m². At a median follow-up of 3.3 months, the actual postoperative GFR exceeded the expected GFR by an average of 12.1% (interquartile range, 2.6%-25.2%). When stratified by preoperative GFR >90, 60-90, and <60 mL/min/1.73 m², respectively, the observed GFR exceeded the expected GFR by 4.3%, 12.6%, and 14.9%, respectively (P = .16). This trend was maintained when GFR was plotted over time. Conclusion After nephrectomy, the remaining kidney exceeded the expected postoperative GFR by 12% in this cohort of patients with preoperative renal scans. Patients with existing renal insufficiency had the greatest compensatory response, and this was durable over time.