Diuresis and voiding pattern in healthy schoolchildren.

OBJECTIVE: To analyse how differences in diuresis affect the normal pattern of micturition of healthy children.

SUBJECTS AND METHODS: Two hundred and six healthy continent schoolchildren, aged 7-15 years, completed a frequency/volume chart for 24 h by recording the time and volume of each micturition. Several diuresis variables were calculated from these charts and compared with sex, age, oral fluid intake, functional bladder capacity, voiding intervals and volumes.

RESULTS: The weight-corrected mean diuresis per 24 h varied 10-fold between individuals, independently of recorded fluid intake. In the majority, the diuresis decreased during the night, but the opposite diurnal pattern occurred in 12% of the children. The individual night-time diuresis was positively correlated with functional bladder capacity and the daytime diuresis was positively correlated with voiding frequency.

CONCLUSIONS: The weight-corrected diuresis varies many-fold among healthy continent children. A substantial proportion has a reversed diurnal pattern with a larger diuresis during the night. The individual bladder size is adapted to accommodate their typical nightly urine production.