Prediction of post‐operative glomerular filtration rate after nephrectomy for renal malignancy

The importance of a correct estimation of contralateral renal function in cases of renal malignancy is obvious, necessitating a conservative approach to tumour resection when function of the contralateral kidney is markedly reduced. The aim of the present study was to determine the accuracy of preoperative gamma camera renography and ⁵¹Cr‐EDTA clearance to predict the glomerular filtration rate (GFR) early and up to 6 months after nephrectomy for renal malignancy. Patients (n=40) underwent both gamma camera renography (^99mTC‐DTPA) and ⁵¹Cr‐EDTA clearance preoperatively, whereas ⁵¹Cr‐EDTA clearance was measured within 1 week and up to 6 months after nephrectomy. The single kidney GFR values of the contralateral kidneys were estimated preoperatively and then compared with the post‐operative ⁵¹Cr‐EDTA clearance values. The predicted GFR values were lower compared with the measured post‐operative ⁵¹Cr‐EDTA clearance values (45 ± 2 vs. 54 ± 3 ml min^–1 1 week after nephrectomy and 53 ± 3 ml min^–1 6 months later, P<0·01, respectively). The difference between the measured and predicted GFR was larger in patients below the median age of 60 years (P<0·05) and confined to patients with a relative uptake of >30% by the tumour affected kidney. Prediction of post‐operative GFR by non‐invasive renal function tests performed prior to surgery for renal malignancy underestimate post‐operative GFR when the function of the tumour affected kidney is preserved, indicating an adaptive GFR increase in these cases.