Measurement of Glomerular Filtration Rate in Man Using DTP A- ^{99 m}Tc

Abstract

The aim of this study was the evaluation of the mechanism of renal excretion of DTPA-^99mTc in man. For this purpose the renal clearances of DTPA-^99mTc and diatrizoate-¹³¹I were simultaneously determined in 21 patients by means of vesical catheterization and of continuous venous infusion of the tracers. The mean ratio between the clearances of DTPA-^99mTc and diatrizoate-¹³¹I was 0.92 ± (SD) 0.06 (p < 0.001). In order to demonstrate a possible tubular reabsorption of the studied tracer, its clearance was determined simultaneously with those of diatrizoate-¹³¹I and urea in 10 patients at different urine flow rates, i. e., under basal conditions and at high urine flow induced by hydration. In contrast to the urea clearance, changes in urine flow rate did not significantly affect the clearances of either tracer. In 12 patients the clearance of DTPA-^99mTc was also determined by means of external counting over the bladder. The mean ratio between the clearances obtained by external counting and by vesical catheterization was 1.03 ± (SD) 0.05. These results demonstrate that the renal clearance of DTPA-^99mTc is slightly lower than the glomerular filtration rate as measured by diatrizoate-¹³¹I. Since its clearance may be easily measured by means of the noninvasive method of external counting over the bladder, DTPA-^99mTc represents a valuable tool in the determination of glomerular filtration rate in man.