The reliability of Tc-99m-DMSA scintigraphy in obstructive uropathy: is late scanning at 24 hours necessary?

Summary

Differential kidney function is usually studied by quantification of relative renal uptake at 2–4 h after injection of the radiopharmaceutical^99mTc-dimercaptosuccinic acid (DMSA). The outcome of this measurement, however, may be unreliable in cases of obstructive uropathy. The obstructed kidney may retain the radiopharmaceutical in the dilated system, which may lead to relatively high values for functioning cortical mass. In this situation, determination of the split kidney function at 24 h instead of 4 h after application of^99mTc-DMSA has been advocated. In order to compare results at 4 h and 24 h an investigation was performed in 8 patients with obstructive renal disease present for more than 2 weeks, and in 7 patients who did not suffer from obstruction. In these 15 patients the differential function measured at 4 h and at 24 h was the same. From our results we conclude that overestimation of the function of an obstructed kidney by^99mTc-DMSA scanning at 4 h is not a major problem. According to the literature, however, in cases of acute obstruction or “complicated” obstruction with stones or infection,^99mTc-DMSA scintigraphy can underestimate the potential function of the obstructed kidney.