To evaluate bladder capacity in women with idiopathic overactive bladder syndrome (OAB) through bladder diary, cystomanometry, and uroflowmetry and assess the concordance of the different measures of bladder capacity. A secondary objective is to describe the relationship between bladder capacity and urinary frequency in OAB patients.

An observational cross-sectional multicentric study was conducted, including female patients diagnosed with idiopathic OAB. All participants underwent a urodynamic study and completed a 3-day bladder diary (3dBD). Different parameters were used to calculate bladder capacity: maximum cystometric capacity (MCC) assessed at the end of filling cystometry, voided volume (VV) during the uroflowmetry, maximum voided volume (VVmax), and average voided volume (VVmed), both assessed through the 3dBD. Reproducibility analysis was performed to assess the agreement among the different bladder capacity measures. Intraclass correlation coefficient (ICC) and weighted Kappa index were used. Bladder capacity parameters were also assessed in relation to urinary frequency.

Bladder capacity measures were diminished in this population, except for VVmax. Poor correlation was found between the different bladder capacity variables (ICC and weighted Kappa index <0.4). Twenty-four-hour frequency and average VV present a weak negative linear relationship (Pearson coefficient −0.344).

MCC and average VV are reduced in OAB patients. MCC does not correlate well with functional bladder volumes determined by voiding diary in the OAB population.