The obstructive index in antenatal unilateral pelviureteric junction obstruction: A novel predictor of the failure of conservative management.

Background: To find the impact of the obstructive index (OI) as a predictor of management in antenatal pelviureteric junction obstruction.

Methods: Records of 135 cases of antenatally detected unilateral pelviureteric junction obstruction, selected for initial observation were retrospectively analyzed. All patients who underwent pyeloplasty on follow up were assigned to Group A. Those patients who were still on conservative management were assigned to Group B. The pelvic anteroposterior diameters of the affected (PAPD[A]) and normal kidney (PAPD[N]) of the same patient, along with the cortical thickness of the affected kidneys (CT[A]) and normal kidneys (CT[N]) on postnatal ultrasound scan, the T1/2 of the affected (T1/2 [A]) and normal kidneys (T1/2 [N]), the differential renal function (DRF), and the shape of the curve on a diuretic renogram were noted for each patient at 6 weeks. The OI was defined as (PAPD[A] × T1/2 [A]) / (PAPD[N] × T1/2 [N]).

Results: The median duration of follow up was 55 months (36-110). Median age at surgery was 12 months (4-80). Group A had 30 patients with 105 in Group B. On multivariate analysis, OI and shape of curve predicted need for surgery with statistical significance. Median OI in Group A was 18.9 compared to 4.82 in Group B (P < 0.001, Mann-Whitney). Using receiver operating characteristic analysis, the area under curve for the OI was 0.95. A level of 12.2 could predict failure of conservative management with a sensitivity of 93.3% and a specificity of 92.4%.

Conclusions: The OI can reliably predict the need for surgery at a very early stage, thus avoiding repeated tests and saving time.