Renal function reserve in children with posterior urethral valve: a novel test to predict long-term outcome

Commonly used measures such as serum creatinine level and glomerular filtration rate do not actually reflect decreased total number of nephrons. There is a need to identify early the subset of patients who are at increased risk for renal failure.

We studied children diagnosed with posterior urethral valve at our institution between August 2007 and December 2008. Renal function reserve was measured at least 6 weeks after initial fulguration of posterior urethral valve. Glomerular filtration rate was obtained by calculating plasma clearance of (99m)technetium labeled diethylenetriamine pentaacetic acid. Renal function reserve was calculated as the difference between stimulated (after protein load) and baseline glomerular filtration rate, and reported as percentage increase in baseline glomerular filtration rate. Patients were divided into 2 groups depending on the presence (group 1) or absence (group 2) of renal function reserve. Less than 10% increase in renal function reserve after protein load was defined as absence of renal function reserve.

A total of 25 children with a median age of 30 months (range 24 to 60) were studied. Median serum creatinine at presentation and nadir value were 1.53 mg/dl (range 0.6 to 4.0) and 0.75 mg/dl (0.6 to 1.0), respectively. Mean ± SD baseline glomerular filtration rate was 59.88 ± 10 ml/min/1.73 m(2) body surface area (range 22 to 124). Mean protein load induced renal function reserve was 32.23% (range 2.3% to 96.70%). After protein load glomerular filtration rate increased in 16 patients (64%) by a mean of 32.23%, remained unchanged in 4 (16%) and decreased in 5 (20%) by a mean of 12.5%. Patients with absent renal function reserve had a greater degree of bladder dysfunction on urodynamic study and more severe vesicoureteral reflux (grade III or higher, p <0.05). At a median followup of 13 months (range 7 to 36) median serum creatinine was 0.78 mg/dl and 1.3 mg/dl in the 2 groups, respectively (p <0.05).

In more than a third of patients with posterior urethral valves renal function reserve is completely depleted at presentation. Decreased or absent renal function reserve may be used as an early indicator of long-term renal deterioration.