Role of calculated glomerular filtration rate using percutaneous nephrostomy creatinine clearance in the era of radionuclide scintigraphy

CONTEXT Gates method tends to over-estimate glomerular filtration rate (GFR) in borderline functioning kidneys. We study the role of calculated GFR in these cases in decision-making regarding performing kidney-sparing surgery or nephrectomy. AIMS The aim of this study is to find the correlation between GFR calculated by percutaneous nephrostomy (PCN) urine creatinine clearance in obstructed kidneys and GFR by radionuclide scintigraphy. It also studies the role of this calculated GFR in borderline functioning kidneys. SETTINGS AND DESIGN Single tertiary care center; retrospective. MATERIALS AND METHODS A total of 46 patients in whom PCN was inserted as an emergency measure in an obstructed kidney and for whom diethylene-triamine-penta-acetic acid/ethylene-di-cysteine (DTPA/EC) scan was also done (Gates method) were analyzed retrospectively. PCN creatinine clearance was calculated for 3 consecutive days, and the mean value was used. STATISTICAL ANALYSIS USED Pearson's correlational analysis; Chi-square test. RESULTS Overall strong correlation was found between the two GFR values (Pearson's r = 0.540692, P < 0.001). Totally 26 patients (56.52%) had comparable GFR values (P > 0.05). Among the 36 patients with borderline functioning kidneys, DTPA/EC scan significantly over-estimated GFR in one-third of the patients. The management plan was changed in 7 out of those patients (46.67%), with nephrectomy performed in all instead of kidney-sparing procedure. When the highest value of calculated GFR was compared, 28 patients had comparable GFRs (60.87%). CONCLUSIONS GFR based on radionuclide scintigraphy may be insufficient for evaluation of residual renal function to determine the management of obstructed kidney with borderline function. For adequate decision-making, other factors including creatinine clearance via PCN should also be considered. Gates method tends to overestimate GFR as compared to calculated creatinine clearance at low GFR levels.