Validation of modified diuretic drainage times criteria in congenital hydronephrosis

Introduction and objective: The value of diuretic renography drainage times in congenital hydronephrosis (AHN) decision making is controversial. Recently, a group suggested a modification to the classically described diuretic drainage time cut-off values. They found that a drainage half-time (T_1/2) < 5 min was normal whereas a T_1/2 exceeding 75 min predicted pyeloplasty. In addition, they reported on the benefit of a delayed drainage image obtained with gravity assistance. We sought to evaluate the ability of these modified T1/2 criteria to predict pyeloplasty, alone or in combination with a delayed drainage image referred to as Global Washout (GWO).

Methods: We retrospectively reviewed 113 patients, including consecutive pyeloplasties for AHN from 2004 to 2018. Patients who underwent pyeloplasty due to low differential renal function (DRF) < 30% or infection were excluded. The control group comprised high grade AHN managed non-operatively. The initial renal ultrasound and MAG 3 Lasix renogram were reviewed for grade, differential renal function (DRF), T_1/2 and GWO. A ROC curve was used to evaluate the T_1/2 and GWO cut-off points that can predict pyeloplasty, using a p-value of less than 0.05.

Results: The pyeloplasty group consisted of 62 patients and the control group consisted of 51 patients. Two patients (3%) in the pyeloplasty group had a T_1/2 < 5 min whereas 21 (34%) had T _1/2 > 75 min (p < 0.001). In the control group, 25 patients (49%) had T _1/2 < 5 min and none had T_1/2 >75 min (P < 0.001). The ROC curve for T_1/2 < 5 min demonstrated 94% sensitivity and 51% specificity whereas a T_1/2 >75 min demonstrated 100% specificity and 34% sensitivity. Analysis of the GWO using a ROC curve revealed that a cut-off of 50% GWO has 100% specificity and 52% sensitivity for pyeloplasty. Overall, a T1/2 > 75 min or GWO <50% predicted 53% of pyeloplasties (Fig A) and was absent in all conservatively managed cases.

Discussion: The limitations of the present study include its retrospective nature. Secondly, the lack of a gold standard diagnostic test for uretero-pelvic junction obstruction hampers objective quantification of diagnostic test utility performance.

Conclusions: We confirm the utility of the modified diuretic half-time criteria and delayed gravity assisted imaging. A T1/2 > 75 min or GWO <50% are indicators of severity whereas a T1/2 of <5 min or GWO >90% is reassuring. Gravity assisted delayed imaging can be especially helpful in cases with indeterminate T 1/2 times and should be included in the standard assessment of hydronephrotic kidneys. These parameters can be used to tailor the frequency and invasiveness of imaging within observation protocols.