The use of quantitative gravity-assisted drainage in diuresis renography

Full text: The purpose of the study was to evaluate the use of quantitative gravity-assisted drainage (GAD) using > 50% residual activity as an indicator to confirm obstruction in diuresis renography in the investigation of hydronephrosis and hydroureteronephrosis. This was evaluated in two groups: (1) frusemide half clearance time T1/2 > 20 min (obstructed range) and (2) T1/2 = 10-20 min (indeterminate range). A retrospective study was performed in 185 patients over a 2-year period. There were 142 males and 43 females with ages ranging from 2 days to 16 years (median age of 26 weeks). 120 F + 20 and 65 F + 0 studies using 99Tcm-MAG3 and frusemide were evaluated. At the end of the 20 min diuretic phase, a post-GAD image was obtained and percent residual activity was calculated by comparison with the last frame of the diuretic phase. GAD > 50% residual activity was used to confirm obstruction in patients where T1/2>20 min and T1/2=10-20 min. These results were compared to the final diagnoses of either surgical findings or conservative management with follow-up of 6-12 months. There were 240 hydronephrotic renal units for analysis with 10 units showing no function: 117 units with T1/2< 10 min; 62 units with T1/2> 20 min; and 51 units with T1/2= 10-20 min. Of the 117 units with T1/2< 10 min, there was only one case of obstruction. Using GAD > 50% residual activity for obstruction in units with T1/2> 20 min, there was a sensitivity of 88.4%, specificity of 73.7% and accuracy of 83.9%. Similarly for units with T1/210-20 min, there was a sensitivity of 100%, specificity of 77.3% and accuracy of 80.4%. In conclusion, the quantitation of GAD>50% residual activity can help to differentiate between obstruction and non-obstruction in renal units with T1/2> 20 min and T1/2= 10-20 min. There is little use of quantitation of GAD when T1/2 < 10 min