The role of Plasma Renin Activity in prenatally diagnosed non-obstructed hydronephrosis at risk for surgery—an observational study

Background Patients with asymptomatic prenatally diagnosed hydronephrosis may progress to needing surgery; no biomarker supporting the identification of these cases is currently available. The aim of the study was to assess the role of Plasma Renin Activity (PRA) as a discriminatory factor to identify patients with asymptomatic prenatally diagnosed hydronephrosis who require close monitoring and are at-risk for surgery. Methods The study group consists of 30 children prenatally diagnosed with asymptomatic unilateral hydronephrosis, initially managed with medical follow-up. Pyeloplasty was indicated if patients became symptomatic or if there was a significant drop in split renal function (SRF) during follow-up. An association was sought between PRA and renal parameters in post-hoc analysis. Results During the mean follow-up of 55.5 ± 8.2 months, 13/30 (43.3%) patients developed delayed drainage and 8/30 (26.6%) underwent pyeloplasty. Mean PRA was higher at presentation in the group which later presented with a drop in differential kidney function ≥ 10%, while it was within the normal range for age in the other patients. Before pyeloplasty, progression to delayed drainage coincided with a drop in SRF and a rise in PRA. While PRA levels normalized after pyeloplasty, SRF improved but did not reach initial values. A mean rise of 68.9% in PRA preceded current indications for surgery by 27.5 ± 9.5 months. Conclusions A progressive increase in PRA in children with asymptomatic prenatally diagnosed hydronephrosis reflects obstructive stress in the tubulo-interstitial compartment. This stress is relieved by pyeloplasty and is reflected by a drop in PRA after surgery. PRA can, thus, serve as the discriminatory factor to identify hydronephrosis patients ‘at-risk’ for surgery even before the current criteria for pyeloplasty are met.