Accuracy of total bladder volume and residual urine measurements: comparison between real-time ultrasonography and catheterization.

The practical value of ultrasonography as a rapid means to accurately determine total bladder volumes and residual urine volume was assessed. Transverse and sagittal bladder diameters were measured with real-time ultrasonography in 50 women: (1) before uroflowmetry, (2) before supine-postvoiding catheterization, (3) before standing catheterization, and (4) after standing catheterization. Calculated bladder volumes, by use of the measured diameters, for each of eight formulas from the literature were compared with their corresponding measured total urine volume, total residual volume, and standing residual volume. The lower limit of ultrasonographic visualization of urine in the bladder was approximately 42 ml. No correlation existed between calculated ultrasound bladder volumes and measured urine volumes for any of the eight formulas. Standing residual volumes were measured in 96% of cases. Ultrasonography cannot as yet rapidly measure bladder volumes accurately. Catheterization remains the best method of assessing postvoid residuals: supine measurements, the gold standard, should be augmented by standing measurements when more accurate volumes are required.