Eight hundred studies of glomerular filtration rate (GFR) measurements were performed by the standard slope-intercept method using ["TcJDTPA and results were compared with a simultaneous measurement of the 3-hr tracer volume of distribution. A wide range of human renal function was studied and a nonlinear relationship between GFR and the volume of distribution resulted with an excellent correlation (r = 0.989). Agreement between the two measured parameters was not constant for all levels of renal function with the greatest accuracy being found for GFR = 60 to 100 ml/min. J NucÃ-Med 28:510-513,1987. here have been a large number of radionuclide methods described for the measurement of glomerular filtration rate (GFR) in the relentless search for more simplified techniques. Constant infusion has been re placed by single injection, urine sampling has been dispensed with, multiple blood sampling has been mod ified to two blood samples or less and, even more recently, bloodless techniques have been described. There has been increasing reliance on assumptions and approximations with each simplification of the original methods. In a recent comparative assessment of the simplified techniques performed simultaneously in 50 patients, we found that in addition to the two-sample, slope-intercept method, only the single-injection, vol ume of distribution method could be recommended as having sufficient accuracy for clinical use (7). Three hours following the injection of a glomerularly filtered agent technetium-99m diethylenetriaminepen-taacetic acid ([99mTc]DTPA),a single blood sample is obtained and the administered dose divided by the plasma concentration at 3 hr to give an apparent vol ume of distribution. From this value, the GFR is cal culated using an experimentally obtained regression equation
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