Differences between nocturics and non-nocturics in voiding patterns: an analysis of frequency-volume charts from...

To evaluate differences between elderly people with and without nocturia (waking up in the night to void) in terms of voiding habits, urine production and voided volumes.

Nocturics or= two voids/night) and non-nocturics (< one void/night) were recruited from a questionnaire survey. Subjects were asked to complete a 3-day frequency-volume chart, including time and volume of each void, and their bedtime and waking time. Diaries from 108 non-nocturics and 116 nocturics were analysed. The number of voids, urine production, largest and average voided volumes were analysed using repeated-measures analysis of variance models, controlling for variables such as age, gender, body weight and gender-diagnosis interaction.

Nocturnal urine volume was higher in nocturics than in non-nocturics. The difference between the groups was larger among the men (estimated difference 384 mL) than among the women (227 mL), but highly statistically significant (P < 0.001) in both genders. Among the men the diurnal urine and 24-h urine volumes were significantly higher in nocturics (difference, diurnal 131 mL, 24-h 462 mL, both P < 0.001). In the women the diurnal urine volume was lower in nocturics than in non-nocturics (difference 147 mL P = 0.0022) with no difference detected in 24-h urine volume. The largest voided volume was significantly less in nocturics than in non-nocturics; the difference was larger in women (128 mL, P < 0.001) than in men (42 mL, P = 0.0027). The average voided volume was 85 mL less (P < 0.001) in nocturics. The overlap between the groups in nocturnal urine and voided volumes was substantial and several significant covariates identified. The ratio between nocturnal urine volume and largest voided volume was the most statistically significant predictor of the number of nocturnal voids.

Elderly nocturics had a higher nocturnal urine production and lower volume per void than non-nocturics. Differences between nocturics and non-nocturics in urine production and largest voided volume did not follow the same pattern in men and women. Nocturia was a result of a mismatch between nocturnal urine volume and largest voided volume, rather than abnormal values in either. The treatment of nocturia should be directed at one or both of these factors, depending on the findings from the 3-day frequency-volume chart of the individual.