To systematically summarize the available evidence concerning the impact of pyeloplasty on symptoms and differential renal function (DRF) in adults with unilateral UPJO in poorly functioning kidneys (PFK), and to identify potential predictors of kidney function recovery that could help clinicians select candidates for pyeloplasty.

A literature search (MEDLINE, Embase, Google Scholar, Scopus, ClinicalTrials.gov, and the WHO Clinical Trials Registry) and systematic review were performed up to September 2020 according to the PRISMA guidelines. PFK were defined as a baseline DRF ≤30% on renal scintigraphy. The primary endpoints were symptom relief and postoperative scintigraphic DRF. Predictors of kidney function recovery were evaluated and compared among studies.

Nine studies comprising 731 patients met the inclusion criteria and were included for evidence synthesis. A DRF increase >5% occurred in 13.3%-53.8% of 160 patients with a pre- and postoperative renal scan. Symptoms improved in 73.3%-93.3% of 141 adults after pyeloplasty. Neither patient's age, baseline DFR, comorbidities, degree of hydronephrosis, kidney parenchymal thickness, nor kidney biopsy findings consistently predicted a significant DRF increase among 375 patients undergoing pyeloplasty.

Based on a low level of evidence, pyeloplasty may relieve symptoms and stabilize kidney function in adults with UPJO in PFK. A significant number of patients showed a DRF increase >5%, yet no consistent predictor of kidney function recovery was identified. Until more evidence becomes available, pyeloplasty could be considered for selected cases after accounting for the risks of a failure requiring a future nephrectomy.