Borg, Kamperis, Olsen, and Ritting (2017) set out to evaluate the nighttime bladder capacity in children with normal daytime bladder capacity and bedwetting. They described estimated bladder capacity as their age plus 1. (i.e. 5 year old + 1 = 6 ounce bladder). Eighty-four percent of the kids had a wet night with a volume less than their daytime bladder capacity. Of these children with decreased nighttime bladder capacity only 11% responded to desmopressin.
My opinion: While I often obtain a daytime voiding diary to get a general idea of a patient’s bladder capacity, I do not obtain a night time bladder capacity diary (wet diaper + first morning urine – dry diaper). It might be difficult to get a family to complete the homework with a scale. This could help with choosing the right pathway for a patient instead of trial and error with alarm, desmopressin (reduce urine volume) or oxybutynin (increase bladder capacity). If a family would like to use medication instead of alarm therapy this could be a nice exercise to decide.
Borg, B., Kamperis, K., Olsen, L., & Rittig, S. (2018). Evidence of reduced bladder capacity during nighttime in children with monosymptomatic nocturnal enuresis. Journal of Pediatric Urology, 14(2). doi:10.1016/j.jpurol.2017.09.021