Intra-individual variability in nighttime urine production and functional bladder capacity estimated by home recordings in patients with nocturnal enuresis

Purpose: We evaluated the intra-individual variability and reproducibility of nighttime urine production on wet nights and functional bladder capacity estimated by long-term home recordings of monosymptomatic nocturnal enures is. In particular, the intention was to evaluate the validity of 1 versus 2 weeks of recording when estimating urine volume on wet nights and 1 versus 2 weekends of recording when estimating functional bladder capacity. Materials and Methods: We analyzed 120, 2-week home recordings of nighttime urine volume from patients with monosymptomatic nocturnal enuresis 6 to 16 years old (mean age 9.1) with at least 3 wet nights per week. Most patient s were nonresponders or partial responders to desmopressin. Nighttime urine volume was estimated by weighing diapers before and after sleep, and measu ring morning urine volume. Of the home recordings 62 included frequency vol ume charts for 2 weekends, which were evaluated for functional bladder capa city defined as the largest voided volume observed. Results: No significant overall week-to-week differences were observed in a verage urine volume on wet nights and functional bladder capacity. There wa s a large intra-individual variability in all measured variables, which was most pronounced for functional bladder capacity and least pronounced for u rine volume on wet nights. With regard to repeatability, the limits of agre ement of urine volume on wet nights were -32% and 36% (95% confidence inter val) as opposed to -54% and 48% for functional bladder capacity. Conclusions: In this study intra-individual week-to-week estimates of avera ge urine volume on wet nights demonstrated acceptable variability and repea tability in contrast to functional bladder capacity. A reliable estimate of urine volume on wet nights could be obtained by 7 nights of home recording , whereas 4 days of daytime recording were necessary when estimating functi onal bladder capacity. Similar studies of patients who respond to desmopres sin are needed.