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Estimating normal bladder capacity in children
M Kaefer1, D Zurakowski, S B Bauer
1Division of Urology, Children's Hospital and Harvard Medical School, Boston, Massachusetts, USA.
Insights
New formulas accurately estimate normal bladder capacity in children. These practical equations, based on age, improve genitourinary disease evaluation and urodynamic data interpretation for pediatric patients.
Area of Science:
- Pediatric Urology
- Medical Imaging
- Biostatistics
Background:
- Accurate estimation of normal bladder capacity is crucial for diagnosing genitourinary diseases in children.
- Previous studies offered initial estimates, but more practical and precise methods are needed for clinical application and urodynamic interpretation.
Purpose of the Study:
- To develop and validate new, practical, and accurate equations for estimating normal bladder capacity in children based on age.
- To improve upon existing methods for bladder capacity estimation in pediatric populations.
Main Methods:
- Retrospective analysis of radionuclide cystography (RNC) data from over 5,000 children.
- Exclusion of patients with lower urinary tract pathologies to ensure a normal cohort.
- Development of linear and nonlinear regression models to correlate age with bladder capacity.
Main Results:
- A cohort of 2,066 children with normal RNC was analyzed, showing age as a strong predictor of bladder capacity (p <0.0001).
- A nonlinear model (4.5 x age^0.40) was most accurate, leading to two practical linear equations: (2 x age + 2) for <2 years and (age/2 + 6) for ≥2 years.
- While girls had larger capacities, the age-related increase did not significantly differ between sexes.
Conclusions:
- The relationship between normal bladder capacity and age in children is nonlinear but can be effectively approximated by two simple linear formulas.
- These new formulas, derived from a large pediatric cohort, offer improved accuracy and ease of use for estimating bladder capacity compared to previous methods.
- Prospective application confirmed the formulas' accuracy in estimating normal bladder capacity in children.
Purpose:
An accurate estimation of normal bladder capacity can be helpful in evaluating the patient with genitourinary disease and in interpreting urodynamic data. Prior studies have provided initial estimates. We propose 2 new equations that are practical, easy to use and more accurate than those previously published.
Materials And Methods:
We retrospectively reviewed the records of more than 5,000 children undergoing radionuclide cystography at our institution. Radionuclide cystography was conducted by instilling (99m)technetium pertechnetate via gravity drip in awake children. Bladder capacity was believed to be achieved when rate of inflow diminished to a minimal rate, initiation of voiding occurred or significant discomfort was indicated. Patients with vesicoureteral reflux, infravesical obstruction, urinary tract infection, dysfunctional voiding or other lower urinary tract pathology were excluded from the study. Linear and nonlinear regression modeling established the relationship between age and bladder capacity.
Results:
A total of 2,066 children (598 boys and 1,468 girls) had normal radionuclide cystography and were included in the analysis. Analysis of variance demonstrated that increasing age was strongly predictive of bladder capacity (p <0.0001). Because a nonlinear model was the most accurate formula for all ages (4.5 x age(0.40) = capacity [ounces]), 2 practical linear equations were determined: 2 x age (years) + 2 = capacity (ounces) for children less than 2 years old, and age (years) divided by 2 + 6 = capacity (ounces) for those 2 years old or older. Although girls had larger capacities than boys, the rate of increase was not significantly different between them.
Conclusions:
The relationship between normal bladder capacity and age in children follows a nonlinear curve. This nonlinear relationship can be approximated by 2 practical linear formulas that are easy to remember and are derived from a larger population than any prior study. These formulas provided accurate estimations of bladder capacity when prospectively applied to normal patients.