Increased renal function in kidneys with ureteropelvic junction obstruction: Fact or artifact? Assessment by quantitative single photon emission computerized tomography of dimercapto-succinic acid uptake by the kidneys

Purpose: We evaluated whether increased differential renal function on the pentetic acid (DTPA) renogram represents elevated renal function in obstructed kidneys. Materials and Methods: In 10 patients with unilateral ureteropelvic junction obstruction and a differential function of 53% or greater on the DTPA renogram of the obstructed kidney we performed quantitative single photon emission computerized tomography of dimercapto-succinic acid uptake by the kidneys. Results: The absolute uptake of dimercapto-succinic acid was significantly higher in the obstructed kidneys compared to the contralateral normal kidneys (30.0% +/- 7.9 versus 25.3% +/- 8.3, t = 3.6, p <0.01, respectively). The elevated absolute uptake in the obstructed kidneys was due to an increased functional volume compared to the contralateral normal kidneys (126.0 +/- 69.7 cc versus 102.3 +/- 59.2 cc, t = 4.4, p <0.01, respectively). Conclusions: The results suggest that increased relative renal function in hydronephrotic kidneys due to ureteropelvic junction obstruction is not an artifact of the DTPA renogram. It may represent a compensatory mechanism that sometimes may overcompensate resulting in a paradoxical hyperfunctioning kidney.