The prognostic value of relative renal function greater than 51% in the pelvi-ureteric junction-obstructed kidney on 99mtechnetium mercaptoacetyltriglycine study

ObjectiveObstructed kidneys with relative function (RRF) estimates >50% are occasionally noted in 99mtechnetium mercaptoacetyltriglycine renal studies. It is thought that increased RRF might confer some benefit and/or permit delayed intervention. We compared the RRF and absolute renal function, as defined by effective renal plasma flow (ERPF), of obstructed kidneys in the ranges >51%, 40%–50% and <40% RRF before and after pyeloplasty.MethodsTwenty children, median age 13.5 months (range 3 weeks–126 months), satisfied criteria for the diagnosis of PUJ obstruction and estimated function >51% (group 1). Their pre- and post-intervention data were compared with 21 children, median age 2 months (range 1 week–126 months), with PUJ obstruction and 40%–50% RRF (group 2); and 21, median age 6 months (range two days–110 months), with RRF below 40% (group 3). Kidneys showing signs of continuing obstruction after surgery were excluded.ResultsFinal ERPF was negatively related to age: younger children, and those with a higher preoperative ERPF, recovered better than older children and those with a lower ERPF (p < 0.05). Pre- and postoperative mean ERPF in group 1 was 76 (range 21–203) and 102 (6–240) ml/min/1.73 msq respectively. In group 2, these values were 75.2 (30–187) and 130.9 (44–306) ml/min/1.73 msq, and they were 42.6 (5–179) and 80.2 (17–205) ml/min/1.73 msq in group 3. When adjustment was made for preoperative ERPF, there was no evidence that RRF grouping was related to ERPF outcome. The postoperative ERPF of seven of 20 kidneys from group 1 (>51%) was lower than the ERPF before surgery compared to 2/21 in group 2 and 4/21 in group 3, but these differences were not statistically significant (p = 0.25).ConclusionsMost kidneys in each functional range improved when obstruction was relieved. An RRF >51% in the obstructed kidney was not always prognostically beneficial, and may be a warning of impending decompensation in a minority.