Comparison of Tc-99m mercaptoacetyltriglycine and I-131 orthoiodohippurate in the determination of effective renal plasma flow

Recent studies have suggested that Tc-99m-labeled mercaptoacetyltriglycine (Tc-99m MAG-3) is a potential replacement for I-131 orthoiodohippurate (I-131 OIH). The two radiopharmaceuticals were studied in 24 patients with varying degrees of renal impairment, for comparison of effective renal plasma flow (ERPF). All patients were injected intravenously with 2-3 mCi of Tc-99m MAG-3 and 250-300 μCi of I-131 OIH simultaneously in separate arms to avoid any chemical incompatibility. Serial digital images were acquired simultaneously for Tc-99m MAG-3 and I-131 OIH at 10 seconds per frame for 30 minutes. The renogram curve was generated and ERPF value was calculated for each kidney using both radiopharmaceuticals and applying the same computer program (Schlegel's program). In all cases, the Tc-99m MAG-3 and I-131 OIH renogram curves were quite similar. The values of ERPF of Tc-99m MAG-3 were not significantly different from those of I-131 OIH studies (paired t-test, P < .01). The correlation coefficient between the two methods was .95 (P < .001), with a linear regression equation y = 12.96 + 0.995 x, where y = ERPF determined by I-131 OIH and x = ERPF determined by Tc-99m MAG-3. This study indicates that Tc-99m MAG-3 is a useful Tc-99m replacement for I-132 OIH in determination of ERPF and generating renogram curves