Evaluation of functional bladder capacity in Japanese children

Background: Functional bladder capacity is a very important factor in the diagnosis of children with voiding disorders. Because Japanese children are thought to have somewhat smaller functional bladder capacity compared with Western children, the convenient formula (so-called Koff formula) bladder capacity (in ounces) = age (in years) + 2 is not suitable for use in Japanese children. Methods: We measured the bladder capacities of 131 Japanese children aged 5-15 years without clinical voiding pattern abnormalities to develop a practical guideline for the prediction of normal bladder capacity for age. Results: An approximate formula relates age and bladder capacity as: bladder capacity (mL) = 25 x (age (years) + 2). Conclusions: The formula presented is thought to be a useful guide for the diagnosis of small, normal or large bladder capacity and offers information on voiding disorders in Japanese children.