A comparison of maximum cystometric bladder capacity with maximum environmental voided volumes

The aim of the study was, to determine whether maximum cystometric capacity accurately reflects the maximum functional bladder volume in women with urinary incontinence. We performed a retrospective chart review involving 85 women between the ages of 22 and 89 with primary complaints of urinary incontinence. The maximum cystometric capacity as determined by cystometry was compared with the maximum environmental voided volumes as recorded in a 24-hour voiding diary, using Pearson's correlation coefficients and paired t-tests. Patients diagnosed as having a small bladder capacity (< 300 ml maximum volume) based on cystometry were also examined with contingency table analysis to determine whether the bladder volumes in the voiding diaries supported the diagnosis of a small bladder. In 85 subjects the average maximum cystometric capacity was 14.7% less than the maximum volume recorded in the voiding diary. The correlation between the maximum cystometric capacity and maximum functional bladder volume was r = 0.473 (P < 0.001). However, there was a statistically significant difference between the two volumes by paired t-test analysis (P = 0.006). Using cystometry to diagnose small bladder capacity showed a sensitivity of 62.9% and a specificity of 71.2% when using voiding diary volumes as the criterion standard. The positive predictive value was 51.4% and the negative predictive value was 84.0%. These results suggest that whereas the maximum bladder capacity measured by cystometry correlates with maximum environmental bladder capacity as determined by 24-hour voiding diaries, there is a statistically significant difference. The diagnosis of a small bladder should not be based on office cystometry alone.