Furosemide-assisted diuretic sup(99m)Tc-DTPA renography in obstructive uropathy

Diuretic sup(99m)Tc-DTPA renography assisted with furosemide was performed in 45 patients with obstructive uropathy and in 93 patients without obstruction. After hydration of 300 ml of water, 20 mg of furosemide (0.5 mg/kg in children) was injected intravenously 15 min. following 8 mCi of sup(99m)Tc-DTPA administration. To evaluate the effect of furosemide on urinary excretion, the excretion half time (T1/2) was obtained from the faster component on the sup(99m)Tc-DTPA excretion curve by two compartment analysis. T1/2 of upper limit was 2.5 min. 80% of patients with obstruction showed a prolonged T1/2. And 57% of patients with non-obstructive renal parenchymal damage also showed a prolonged T1/2. Therefore, it was difficult to separate the patients with obstructive uropathy from the patients with renal parenchymal damage by the results of prolonged T1/2 alone. However, it became quite helpful to separate these two different patients with prolonged T1/2 by evaluating serial dynamic images and renogram. Although frequently seen in patients without obstruction, ''socalled'' obstructive findings (radionuclide retention in the pelvicalyceal system and obstructive pattern on renogram) were rarely seen in the prolonged T1/2 patients with renal parenchymal damage. With the combined criteria of obstructive findings and prolonged T1/2, 71% of the patients with obstruction were correctly detected, and only 5% of false positives were observed among 93 patients without obstruction. It is suggested that diuretic renography can be useful to differentiate obstructive uropathy from non-obstructive disease in cases of obstructive findings on conventional sup(99m)Tc-DTPA renography. (J.P.N.)