Reproducibility of single-sample clearance of Tc-99m-mercaptoacetyltriglycine and I-131-orthoiodohippurate

Recent literature has questioned whether Tc-99m-mercaptoacetyl-triglycine ( MAG3) clearance measurements are reproducible enough for routine clinical m onitoring of renal function. For many years, we have routinely followed the renal function of patients with spinal cord injuries using a combination o f radionuclide imaging and clearance measurement. Methods: In this study. w e retrospectively review 1626 effective renal plasma flow (ERPF) measuremen ts in 197 patients with paraplegia or quadriplegia performed over a 21-y pe riod, using rat I-131-orthoiodohippurate (OIH) through 1990 and MAG3 since 1991. MAG3 clearance was divided by 0.53 to convert it to ERPF. Reproducibi lity was measured as pooled SD from the single-patient linear regression li nes of ERPF versus time. Results and Conclusion: There was no significant d ifference between MAG3 (SD = 46 mL/min, n = 907) and OIH (SD = 52 mL/min, n = 719). The data were therefore combined to obtain the SD for a single ERP F measurement, which was 49 mL/min. The corresponding coefficient of variat ion was 8.5% of the mean value of 581 mL/min. In our experience, this is ad equate for monitoring the renal function of these patients.