Presentation Authors: Michael Lam*, Casey Seideman, Solange Bassale, Aaron Bayne, Portland, OR
Introduction: Metabolic evaluation of pediatric stone formers includes 24-hour urine collection and analysis. It is generally recommended 24-hour urine collection be performed after a single stone episode in children due to their predilection for identifiable metabolic abnormalities. Within the adult literature there is disagreement on the adequacy of a single collection, and some argue that two should be performed. Using a large multi-institutional database of pediatric stone formers, we evaluated this question in children and hypothesized that a single collection could lead to undertreatment of patients.
Methods: All patients who had two consecutive 24-hr collections performed between 2007-2013 were included. Using established cutoffs in the literature, we determined whether values were classified as normal or abnormal. This included calcium > 4mgkg/day, oxalate > 40mg/1.73m2, citrate < 310/1.73m2 in girls and < 365/1.73m2 in boys, uric acid >0.815 g/1.73m2, calcium phosphate > 2, SS calcium oxalate > 12, and pH < 5.5 or > 6.2. We classified those with two normal or abnormal collections as concordant, and those with two conflicting collections as discordant.
Results: A total of 51 patients underwent two consecutive 24-hr urine collections. Discordance among collections ranged as high as 29.41% (15 children). Urinary calcium was discordant among 14 children (27.45%, Figure). Of those with initial normal collections, we calculated those with abnormal second collections. 27.03% had abnormal calcium values on their second collection despite a normal calcium values on their first collection. Other parameters were 5.13% for oxalate, 12.5% for citrate, 4.17% for uric acid, 17.07% for SS calcium oxalate, 36.36% for calcium phosphate, and 42.86% for pH.
Conclusions: There is a clinically relevant amount of variation in urinary parameters among pediatric patients who undergo 24-hour collections. While we recognize the inconvenience of performing a metabolic evaluations, we believe that two collections should be performed as our data suggest that basing treatment decisions off a single collection may lead to undertreatment of pediatric stone formers.