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The Effects of Obesity on Bladder Capacity in Children with and without Lower Urinary Tract Symptoms


Objectives: Functional bladder capacity is an important factor in the diagnosis of lower urinary tract symptoms (LUTS) in children. LUTS are highly prevalent in children and this prevalence increases in obese children. However, the effects of obesity on bladder capacity are unknown. This study examines the relationship of obesity on functional bladder capacity and LUTS. This study also examines the differences in expected values based on the Koff formula between obese versus non-obese children.

Methods: Demographic data and voiding diary measurements were prospectively collected, after informed consent, for children without LUTS. The same data set was compared to data collected retrospectively for children with LUTS managed at the CHOC Children’s Pediatric Urology Center after ethics approval from the institution. Obesity was defined as children who were above the 95th percentile in gender specific weight by age. Expected bladder capacity was calculated using the Koff formula. Statistical comparison was performed using the Student t-test, where significance was set at p<0.05.

Results: We prospectively screened 110 children without LUTS and enrolled 35 and retrospectively identified 35 children with LUTS. Eighteen of the children without LUTS (25.7%) were non-obese while 17 (24.3%) were obese. In the LUTS group, 19 (27.1%) were non-obese and 16 (22.9%) were obese. Among patients with LUTS, AVV, MVV, and MMVV were not significantly different in obese versus non-obese children (p=0.154, p=0.587, p=0.378, respectively). There was no difference in prevalence of LUTS between healthy weight and obese children (p=1.000). Furthermore, bladder capacity expressed as a percentage of expected bladder capacity (as calculated by the Koff formula) was significantly different between non-obese and obese patients without LUTS (p=0.040).

Conclusion: Although this study has low statistical power due to a small sample size, trends show a lower functional bladder capacity in obese children compared to non-obese children with LUTS. Therefore weight counseling should be included in the management of these children. Additionally, LUTS does not have a higher prevalence in obese children when compared to healthy weight children in this study population. Furthermore, the Koff formula underestimates bladder capacity in obese, non-symptomatic children.

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