Society for Pediatric Urology - Stone disease in obese children resembles the adult population based on a national multi-institutional cooperative assessment of 24-hour urine parameters.

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Stone disease in obese children resembles the adult population based on a national multi-institutional cooperative assessment of 24-hour urine parameters.
Gina M. Cambareri, MD¹, Dana W. Giel, MD², Aaron P. Bayne, MD³, Sean Corbett, MD⁴, Elleson Schurtz, MD², Larisa Kovacevic, MD⁵, Troy Sukhu, BS⁴, Ross Wopat, MD³, George Chiang, MD⁶.
¹UCSD Department of Urology, San Diego, CA, USA, ²University of Tennessee Health Science Center/Le Bonheur Children's Hospital, Division of Pediatric Urology, Memphis, TN, USA, ³Oregon Health Sciences University, Department of Urology, Portland, OR, USA, ⁴University of Virginia, Department of Urology, Charlottesville, VA, USA, ⁵Children's Hospital of Michigan, Department of Urology, Detroit, MI, USA, ⁶UCSD Department of Urology, Rady Children's Specialists of San Diego, San Diego, CA, USA.

Title
Stone disease in obese children resembles the adult population based on a national multi-institutional cooperative assessment of 24-hour urine parameters.
Introduction and Objectives:
The incidence of pediatric stone disease is rising across the United States. Herein we analyzed the 24-hour urinary parameters in children with nephrolithiasis across four institutions with particular emphasis on their relationship to body mass index (BMI).
Methods
The 24-hour urinary parameters obtained from children with nephrolithiasis seen between 2000-2013 were stratified by BMI percentile ≥85 and <85 (overweight and obese patients versus healthy weight, respectively). Exclusion criteria included patients with a history of spina bifida, neurogenic bladder, cerebral palsy and patients on medical treatment before the first 24-hour urine collection.
Results
206 children (females=51.9%) with a mean age of 13± 3.9 years met the inclusion criteria and were further analyzed. Overweight and obese patients consisted of 35.4% of the cohort. Metabolic abnormalities were present in 130 children (63.1%). All 24-hour urinary values were adjusted for weight or body surface area. The institutions were well matched with respect to metabolic disorders present, with hyperoxaluria in 15.5%, hypocitraturia in 14.6%, hypercalciuria in 16.0% or a combination of metabolic abnormalities in 17.0%. Low volume was present in 48.5%.
Univariate analysis was performed and revealed that overweight and obese children were more likely to have low urinary volume and isolated hyperoxaluria compared to normal weight children (Table). On multivariate analysis children considered overweight or obese were more likely to have low urinary volume (OR 3.863, 95% CI 1.959-7.619, p<0.0001) and isolated hyperoxaluria (OR 2.133, 95% CI 1.032-4.408, p=0.0409) compared to normal weight children.
Table: Univariate Analysis, BMI Percentile <85 vs ≥85
BMI Percentile P-value
<85th Percentile ≥85th Percentile
n=133 n=73
Volume 0.0008
Low Volume (<20ml/kg/day) 53(39.9) 47(64.4)
Normal (>20 ml/kg/day) 80(60.1) 26(35.6)
Hyperoxaluria 0.0021
Yes (>40mg/1.73m^2/day) 13(9.8) 19(26.0)
No (<40mg/1.73m²/day) 120(90.2) 54(74.0)
Results are presented as n(%)

Conclusion
Although there is a link between stone formation and BMI in adults, no definitive conclusions have been proven in the pediatric literature. Herein we report the first multi-institutional study evaluating 24-hour urinary parameters in children across the US in different regions. This represents a national profile of 24-hour urines in pediatric stone formers, which is consistent across multiple institutions. Our study indicates that children who are overweight or obese are more likely to have low urinary volume and hyperoxaluria compared to normal weight children. We speculate that dietary factors may represent a major cause of urolithiasis in this population.

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