The impact of daytime diuresis on voiding frequency and incontinence classification in children.

Purpose: Daytime voiding frequency is an important criterion in the classification of childhood incontinence. The aim of this study was to assess the relative impact of diuresis and bladder capacity on voiding frequency.
Materials and Methods: We analyzed data from 570 children 4 to 15 years old (median age 8.3 +/- 2.0 years) treated for urinary incontinence at a secondary referral center, and 87 healthy controls. Based on frequency-volume charts, daytime voiding frequency, age adjusted maximum voided volume, daytime diuresis and fluid intake were calculated. Children were classified according to voiding frequency into 3 groups-decreased (fewer than 3 voids daily), normal (3 to 7) and increased voiding frequency (more than 7).
Results: A total of 219 children had monosymptomatic enuresis, while 351 children presented with daytime symptoms. In children with daytime symptoms we found a significant difference between voiding frequency groups regarding daytime diuresis (decreased voiding frequency 12.3 +/- 4.1 ml/kg, normal 18.7 +/- 6.0 ml/kg, increased 31.1 +/- 9.8 ml/kg, p <0.001). In contrast, maximum voided volume observed/expected bladder capacity for age did not differ significantly between normal and increased frequency groups (72% +/- 25% vs 74% +/- 23%), compared to patients with decreased voiding frequency (89% +/- 30%, p <0.01). Also, in healthy children we found a positive correlation between voiding frequency and daytime diuresis, whereas maximum voided volume observed/expected bladder capacity for age did not correlate with voiding frequency. Furthermore, we observed a significant positive correlation between fluid intake and diuresis (r = 0.53, p <0.001).
Conclusions: In healthy controls and children with incontinence daytime voiding frequency depends mainly on diuresis, and seems less influenced by bladder capacity. Diuresis should be taken into consideration when evaluating voiding frequency from frequency-volume charts in children.