Bladder diary volume per void measurements in detrusor overactivity

Purpose: We investigated the clinical usefulness of adjusting reference volume per void values for a recently reported strong tendency for volume per void to increase with increasing 24-hour volume in asymptomatic individuals. Our approach was to 1) test whether the adjustment increases the separation between volume per void measurements in patients with detrusor overactivity and an asymptomatic reference population, and 2) compare by regression analysis volume per void vs 24-hour volume relationships in patients with detrusor overactivity and asymptomatic volunteers. Materials and Methods: We studied 3-day bladder diaries in 29 patients with detrusor overactivity and without genuine stress incontinence, an age matched control group of 29 asymptomatic women and a reference population of 161 asymptomatic women. Minimum, maximum and average volume per void measurements were calculated. The incidence of volume per void measurements below the 10th reference percentile was used as the measure of separation between the detrusor overactivity and asymptomatic populations. Results: In patients with detrusor overactivity volume per void showed a highly significant positive relationship to 24-hour volume (p < 0.0005). However, patient data points tended to lie below and parallel to control data points. Adjusting for the 24-hour volume relationship significantly increased the incidence of volume per void measurements below the 10th reference percentile in patients with detrusor overactivity (p < 0.01). Conclusions: Adjusting for the 24-hour volume relationship increased the separation of patients with detrusor overactivity volume per void measurements from the reference population. Adjusting volume per void percentiles for the 24-hour volume relationship decreased the incidence of false-negative volume per void percentiles above the 10th percentile in patients with detrusor overactivity and false-positive volume per void percentiles below the 10th percentile in asymptomatic volunteers.