Correlation of 1-125 lothalamate and Tc-99m DTPA Measurements of GFR Using the Single Injection Method

Abstract

Simultaneous renal imaging and determination of GFR [glomerular filtration rate] can be obtained by using 99mTc-diethylenetriaminepentaacetic acid [DTPA]. To assess the accuracy of the GFR value, a comparison was made between commercial sources of 99mTc-DTPA and 125I-iothalamate. The calculation assumed monoexponential loss of each radiopharmaceutical from the renal compartment. Plasma measurements were made at 2 sampling intervals, 90-120 and 180-240 min. An apparent volume of distribution calculated for plasma concentrations at 2 and 3 h was examined as a single sample indication of GFR. GFR values appear to be higher with DTPA than with iothalamate at the earlier interval. Choice of the later sampling times may be desirable for patients with known renal disease. The apparent volume of distribution at 3 h may be a convenient single sample for monitoring or surveying patients for renal disease.