The accuracy of portable ultrasound scanning in the measurement of residual urine volume.

The accuracy of 2 successive models of a portable (2.5 kg.) ultrasound unit in determining residual urine volumes in 100 patients was assessed. Ultrasound measurements were compared to post-scan bladder volumes obtained by catheterization and fluoroscopic screening in the same patients. The first ultrasound unit (group 1, 50 patients) showed correlation with residual volumes of 0.86 (R2 = 0.73) and a mean difference from the true residual volume of 41 ml. (95% confidence interval 26 to 55 ml.). The second ultrasound unit (group 2, 50 patients) showed correlation with residual volumes of 0.97 (R2 = 0.94) and a mean difference from the true residual volume of 24 ml. (95% confidence interval 17 to 31 ml.). The differences in volumes were significantly lower with scanner 2 (t = 2.02, p = 0.047). The mean difference between catheter volume estimate and true bladder volume was 25 ml. (95% confidence interval 16 to 34 ml.). The accuracy of the BladderScan BVI 2500+ scanner is as good as catheter estimations of true residual volume and is sufficient to recommend its use as an alternative to catheterization for the determination of residual urine volume.