The Significance of Radiopharmaceutical Choice on the Estimation of the Absolute Renal Function in Different Stages of Renal Failure

Objective: An abnormal filtration fraction due to divergence between glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) may lead to different estimations of absolute renal function, depending on the radiopharmaceutical administered. The purpose of this study was to estimate GFR and ERPF by measuring the clearances of technetium-99m diethylenetriamine pentaacetic acid (99mTc-DTPA) and iodine-131 sodium o-iodohippurate (131I-OIH) in patients with renal failure and evaluate the significance of these radiopharmaceuticals in the prognosis of the disease. Methods: This study included 25 patients who were followed up during different phases of acute renal failure (ARF) as well as 46 patients with incipient and advanced chronic renal failure (CRF). Results were compared with those obtained in 20 healthy volunteers. Clearance of 99mTc-DTPA and 131IOIH was measured by the technique of a single blood sample taken 180 and 44 min after administration of the radiotracer, respectively. Results: In the patients with ARF, absolute values of GFR and ERPF decreased during oligoanuric and diuretic phases, but the lower filtration fraction suggested a greater reduction of GFR. In the recovery phase of ARF, both GFR and ERPF improved and an almost normal filtration fraction suggested a more prominent GFR increase. The recovery of ARF patients was in accordance with 131I-OIH clearance values recorded in the oligoanuric phase. The GFR and ERPF decreased concordantly in patients in the incipient stage while in advanced CRF, a slightly greater decrease in GFR was recorded. Conclusions: In ARF, the degree of the initial fall in GFR does not serve as a prognostic indicator whereas the degree of the initial fall of ERPF does have prognostic significance. The decrease in GFR parallels the decrease in ERPF in CRF and a measurement of either parameter should give a comparable estimate of