Diuretic renography with the addition of quantitative gravity-assisted drainage in infants and children

The aim of this study was to evaluate the use of quantitative gravity-assis ted drainage (GAD) using >50% residual activity as an indicator to confirm obstruction in diuretic renography in the investigation of hydronephrosis a nd hydroureteronephrosis in infants and children. This was evaluated in 2 g roups: furosemide clearance half-time (t(1/2)) > 20 min (obstructed range) and t(1/2) = 10-20 min (indeterminate range). Methods: Two hundred children (155 boys, 45 girls; age range, 2 d to 16 y; median age, 26 wk) were studi ed over a 2-y period. One hundred thirty-five F+20 (diuretic given 20 min a fter radiopharmaceutical) and 65 F+0 (simultaneous administration of diuret ic and radiopharmaceutical) studies were performed with intravenous adminis tration of Tc-99m-mercaptoacetyltriglycine (MAG3) and furosemide. At the en d of the 20-min diuretic phase, a 5-min post-GAD image was obtained, and th e percentage of residual activity was calculated by comparison with the las t 5 min of the diuretic phase. AII patients were monitored for 6-12 mo, and the final diagnoses were based on either surgical findings or conservative management with follow-up sonography or Tc-99m-MAG3 studies. Results of th e diuretic renography using quantitative GAD were then compared with the fi nal diagnoses. Results: A renal unit was defined as a kidney and its ureter . In the 200 patients studied, 256 hydronephrotic renal units were analyzed : 10 units showed no function, I unit showed poor function, 131 units had t (1/2) < 10 min, 62 units had t(1/2) > 20 min, and 52 units had t(1/2) = 10- 20 min. Of the 131 renal units with t(1/2) < 10 min, there was only 1 case of obstruction. Using GAD > 50% residual activity for the diagnosis of obst ruction in 62 renal units with t(1/2) > 20 min, the sensitivity was 88.4%, the specificity was 73.7%, and the accuracy was 83.9%. Similarly using GAD > 50% residual activity for the diagnosis of obstruction in 52 units with t (1/2) = 10-20 min, the sensitivity was 100%, the specificity was 79.5%, and the accuracy was 82.7%. Conclusion: The quantitation of GAD > 50% residual activity in diuretic renography can help to differentiate between obstruct ion and nonobstruction in renal units with t(1/2) > 20 min and t(1/2) = 10- 20 min. The quantitation of GAD when tin ( 10 min is not useful because obs truction has already been excluded.