Delayed parenchymal transit during Tc-99m MAG3 renography is a valuable sign in diagnosing urinary obstruction in patients with early hydronephrosis

Diuretic renography (DR) can be false negative with upper urinary tract obstruction due to low compliance of the renal pelvis. Delayed parenchymal transit (DPT) may be a valuable sign in case of false negative DR. We compared the diagnostic values of DR and DPT during Tc-99m MAG3 diuretic scan in adults with suspected unilateral obstructive uropathy. Fifty-four patients (male:female=30:24, age: 40.7±15.5 yrs) who underwent Tc-99m MAG3 diuretic scan due to suspicious unilateral obstructive uropathy were analyzed. DR with a T1/2 of > 15 min was considered as positive for obstruction. DPT was considered to be present when there was delayed appearance of radioactivity in the renal pelvis and prolonged retention of radioactivity in the renal pelvis and prolonged retention of radioactivity in the renal parenchyma. The renal area ratio was defined as the ratio of pixel number of hydronephrotic after intervention, or aggravated hydronephrosis without intervention. Non-obstruction was defined as unchanged hydronephrosis over 6 months. Twenty-six renal units had obstruction and 28 no obstruction. The sensitivities of DR and DPT were 69% (18/26) and 50% (13/26) respectively. Two renal units with DPT but negative DR showed DPT had lower renal area ratio than 7 renal units without DPT (0.97±0.20 vs 1.30±0.41, p<0.05). Differential renal function was not significantly different between these groups. DPT correctly diagnosed all renal units with non-obstruction (specificity 100%), while the specificity of DR was 89% (25/28). DPT during Tc-99m MAG3 diuretic scan may be a valuable sign in diagnosing urinary obstruction especially in patients with false negative DR and early HN