113mIn-DTPA, a useful compound for the determination of glomerular filtration rate (GFR). The binding of 113mIn to DTPA and a comparison between GFR estimated with 113mIn-DTPA and 125I-iothalamate

For measurement of glomerular filtration rate the usefulness of diethyl traimino penta acic (DTPA) labelled with 113mIndium has been explored. The labelling procedure is very simple, since eluate from an 113mIn generator can be used directly for labelling DTP. The in vitro and in vivo binding of 113mIn to DTPA in competition with serum proteins was studied by gel-filtration. The radioactivity with the 113mIn-DTPA peak represented 100.6, 107.1 and 99.6% of the amount of radioactivity applied to the gel column for the in vivo studies, and 102.0 and 101.4% for the in vitro studies. Futhermore, the clearance of 113mIn-DTPA was compared to the clearance of 125I-iothalamate using the constant infusion technique. The clearance values were found to be nearly equal (r=0.996). It is concluded that 113mIn is almost entirely bound to DTPA after intravenous injection of the 113mIn-DTPA complex, and that the complex is a suitable agent for determination of glomerular filtration rate.