Urinary habits among asymptomatic women

The purpose of this study was to determine normal ranges for voiding diary variables for a racially diverse sample of women without lower urinary tract symptoms in the United States.

Three hundred women without lower urinary tract symptoms completed a 24-hour log of fluid intake and volumes voided. We used linear regression to analyze diary data according to patient characteristics, which included race, age, body mass index, and parity.

The following races were represented: black, 118 women (39%); white, 117 women (39%); Hispanic, 36 women (12%); Asian, 28 women (9%); and mixed race, 1 woman (<1%). Subjects voided a median of 8 times in 24 hours; 95% of the subjects recorded fewer than 13 voids per 24 hours. Subjects recorded a median of 4 voids per liter of fluid intake (95% recorded fewer than 9 voids per liter intake) and a median of 5 voids per liter urine output (95% recorded fewer than 12 voids per liter output). Nighttime voids were recorded by 133 subjects (44%). According to current definitions, polyuria was present in 54 subjects (18%). Linear regression showed that the number of voids per 24 hours was related to patient age (beta =.2, P <.001) and fluid intake (beta =.39, P <.001). Mean (beta = -.31, P <.001) and maximum (beta = -.2, P =.003) voided volumes were lower among black women. Voids per liter of fluid intake varied with age (beta =.19, P =.002) and were higher among parous women (beta =.12, P =.003) and Asian women (beta =.17, P =.002). Voids per liter output were lower among black women (beta =.34, P <.001). The number of nighttime voids depended only on patient age (beta =.23, P <.001).

The results of this multiracial study differ materially from other studies of asymptomatic women. It is probably inappropriate to apply a single set of normative values to all women in the United States because of the significant variability in regional climates and populations.