The 24-hour bladder diary is considered to be the gold standard for evaluating maximum voided volume (MVV). However, we observed that patients often have greater MVV during in office uroflowmetry than that seen in the bladder diary. There are two non-invasive methods by which MVV can be determined - at the time of uroflowmetry (Q-MVV), or by a 24-hour bladder diary (BD-MVV). For Q-MVV, the patient is instructed to wait to void until the bladder feels comfortably full. The purpose of this study is to compare Q-MVV to BD-MVV, and to assess the differences between them.

This was an institutional review board approved retrospective study of men and women evaluated for LUTS. A database of 771 patients evaluated for LUTS who completed a 24-hour bladder diary independently using a smartphone application was searched for inclusion into the study.* Exclusion criteria included bladder diaries without a contemporaneous uroflowmetry in the clinical setting, and those with incomplete or erroneous diary entries. Q-MVV and BD-MVV were extracted from the uroflowmetry and 24-hour bladder diary. When multiple uroflowmetries were available, the Q-MVV with the highest Qmax was used. When multiple bladder diaries were completed, the earliest one was used. For Q-MVV, the patient was instructed to wait to void until s/he felt full. Sample means were compared, and Pearson’s correlations were calculated between the Q-MVV and BD-MVV data across the total sample, women, and men. 

*weShare® URO from Symptelligence.com

771 patients with LUTS completed bladder diaries. Of these, 400 patients, 205 women and 195 men, had contemporaneous Q-MVV. On average, the BD-MVV was 123.88 mL greater than Q-MVV (figure 1). In total, there was a weak correlation (Pearson’s r = .34) (figure 2). The difference as a percentage of the larger of the two MVVs was calculated for the 400 patients. Further, in 165 patients, there was a difference ≥ 50% between Q-MVV and BD-MVV.

Although the mean BD-MVV was significantly larger than Q-MVV, the Q-MVV was larger in 21% of patients. Moreover, when calculating the difference between the 2 measurement tools as a percentage of the larger value, we found a discrepancy of more than 50% in 260 of the 400 patients in the sample. This suggests an estimation of MVV may be inaccurate by 50% or more if only one measurement tool is used. Furthermore, there was only a weak positive correlation between the two tools (Pearson’s r = .34). These findings are significant because an assessment of patients’ MVV through the singular use of BD-MVV or Q-MVV may be lacking.

The data suggest that there is a difference between the two measurement tools, and that the BD-MVV was significantly greater than Q-MVV. However, maximum voided volume, whether obtained by Q-MVV or BD-MVV may be inaccurate by 50% or more when only one of these assessment tools is used. For a more reliable assessment of MVV, this study suggests that both Q-MVV and BD-MVV should be assessed and that the larger of the two values is a more accurate assessment.