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-assisted drainage (GAD) using >50% residual activity as an indicator to confirm obstruction in diuretic renography in the investigation of hydronephrosis and hydroureteronephrosis in infants and children. This was evaluated in 2 groups: furosemide clearance half-time (t 1/2) > 20 min (obstructed range) and t 1/2 = 10-20 min (indeterminate range).

Two hundred children (155 boys, 45 girls; age range, 2 d to 16 y; median age, 26 wk) were studied over a 2-y period. One hundred thirty-five F+20 (diuretic given 20 min after radiopharmaceutical) and 65 F+0 (simultaneous administration of diuretic and radiopharmaceutical) studies were performed with intravenous administration of 99mTc-mercaptoacetyltriglycine (MAG3) and furosemide. At the end of the 20-min diuretic phase, a 5-min post-GAD image was obtained, and the percentage of residual activity was calculated by comparison with the last 5 min of the diuretic phase. All 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 99mTc-MAG3 studies. Results of the diuretic renography using quantitative GAD were then compared with the final diagnoses.

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, 1 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 obstruction 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%.

The quantitation of GAD > 50% residual activity in diuretic renography can help to differentiate between obstruction and nonobstruction in renal units with t 1/2 > 20 min and t 1/2 = 10-20 min. The quantitation of GAD when t 1/2 < 10 min is not useful because obstruction has already been excluded.