Accuracy of bladder volume determinations by ultrasonography: are they accurate over entire bladder volume range?

To investigate the accuracy of a portable three-dimensional hand-held BladderScan (BS) and two-dimensional conventional ultrasonography (CUS) in the estimation of bladder volumes.

The bladder volume of 65 subjects was measured during filling cystometry using two ultrasound modalities. Serial measurements were performed when the infused volume reached 100, 200, 300, and 400 mL; the investigator measured the volumes three times each with BS and CUS. Each corresponding true volume was calculated by interpolation using zero volume and the final catheterized volume at the end of cystometry. The accuracy of the two ultrasound methods was compared using raw scaled values of the volumes and the percentage of differences of volume.

Bladder volumes determined by CUS and BS were underestimated by 21.8% and 3.3% (mean values), respectively. The percentage of differences of volume of BS was not statistically significant (P >0.05), but that of CUS was statistically significant (P <0.00001). No significant percentage of differences of volume change according to the volume status was observed by either ultrasound measurement method (P >0.05). Linear regression analysis between the true volumes and the raw scaled volumes showed that the slope of the BS was closer to 1.0 than that of the CUS, and the difference was statistically significant (P <0.001). The effects of diagnosis, age, sex, and body mass index were not significant in determining the bladder volume by either method (P >0.05).

Our results demonstrated that a three-dimensional hand-held scanner measures the bladder volume in a reproducible and accurate manner for a wide range of bladder volumes and is superior to two-dimensional stationary ultrasonography.