Background In children who have undergone both Tc-99m-DMSA and Tc-99m-MAG3 studies for the assessment of differential renal function (DRF) and drainage, respectively, we have noticed good agreement between the calculated DRF values, and hypothesized that there is no significant difference in DRF values calculated from these tests. Therefore, both tests may not always be necessary.
Objective To determine whether there is a statistically significant difference between DRF values calculated using Tc-99m-DMSA and those calculated using Tc-99m-MAG3.
Materials and methods We retrospectively identified children imaged with Tc-99m-DMSA and Tc-99m-MAG3. We recorded DRF values, age, indication, and renal pelvis diameter. For the Tc-99m-DMSA studies we recorded the imaging time after injection. For the Tc-99m-MAG3 studies we recorded the delay between injection and data acquisition, diuretic use and evidence of delayed drainage or reflux.
Results We identified 100 episodes in 92 children where both Tc-99m-DMSA and Tc-99m-MAG3 scans had been performed within a few days. The commonest indication was urinary tract infection or pelviureteric junction obstruction. The mean age of the children was 6.96 years. A significant but clinically acceptable trend was seen between abnormal DRF and difference between tests. A significant link was found with the difference between tests and the time of imaging after DMSA injection, and also with scarring. No significant effect was caused by renal pelvis dilatation, delayed drainage, frusemide administration, or delayed Tc-99m-MAG3 imaging.
Conclusion If a Tc-99m-MAG3 study has been performed then a Tc-99m-DMSA study is unnecessary provided DRF is normal on the Tc-99m-MAG3 study and there is no scarring. A change in practice would lead to considerable savings in time, cost and radiation burden.