Estimation of glomerular filtration rate and bladder capacity: the effect of maturation, ageing, gender and size.

Objective: To show that glomerular filtration rate (GFR) and bladder capacity (BC) develop isometrically, and to provide graphs for estimating GFR and BC for specific individuals of any age, sex, height and weight, for cystometric purposes.
Materials and Methods: GFR and BC data were collected from published reports; graphs relating GFR and BC to age, sex, height and weight were obtained by using a computerized curve-fitting technique that minimizes the 1.1 power of the absolute error.
Results: The plots show the GFR and BC for individuals of 10th, 50th and 90th percentile height and weight as a function of age and sex for different physiological conditions. GFR increases up to age 20 years and thereafter declines, whereas GFR per unit body surface area reaches a maximum at 3.25 years old and declines thereafter.
Conclusions: The clinical management strategy to preserve or enhance renal function in paediatric and adult nephrological disease should incorporate the present data on development, growth, ageing and deterioration of function. These data should be used when interpreting cystometrograms and evaluating compliance. The graphs are useful for clinically estimating GFR and BC, especially when estimating infusion rate and BC for individual patients. BC and GFR develop isometrically with a proportionality constant of 4.56 min, except from birth to 1.5 years of age. Accordingly, individuals with healthy urinary systems, irrespective of age, sex and size, in the same physiological conditions have, on average, the same time to reach BC, ranging from 7 h at a normal 1% GFR to 41 min at the maximum diuresis of 10% GFR.