Purpose: It is unclear whether supranormal differential renal function of the hydronephrotic kidney is real or artifactual. We investigated the effect of clinical and renographic parameters on differential renal function.
Materials and methods: The study included 34 males and 10 females from 1 to 9 months old (median age 2.6 months) with unilateral congenital hydronephrosis. A 99mtechnetium (Tc) mercaptoacetyltriglycine (MAG3) scan was performed, and regions of interest were drawn on the kidneys, and perirenal and lateral backgrounds. Differential renal function was calculated with and without background subtraction at 30-second intervals from 0.5 to 3 minutes after injection of 99mTc-MAG3. The effects of age, sex, obstruction, site and size of the hydronephrotic kidney were analyzed using the generalized estimating equations method.
Results: There were 11 right and 33 left hydronephrotic kidneys. An obstructive renographic pattern was present in 33 cases. The trends of differential renal function according to intervals were different between kidneys with and without background subtraction, and differential renal function increased significantly as size increased (p <0.05). Differential renal function of the hydronephrotic kidney with an obstructive renographic pattern increased with time when perirenal or no background subtraction was applied (p <0.05). The effects of age, sex or laterality on differential renal function were not significant. Supranormal function (differential renal function 55% or greater) was present regardless of background subtraction methods and measurement time.
Conclusions: Differential renal function is higher in larger hydronephrotic kidney but function of the kidney with an obstructive pattern is overestimated on later phases of 99mTc-MAG3 renal scan. Supranormal differential renal function is real and may be pathologic since it is prone to occur in larger obstructive hydronephrotic kidneys.