Residual urine volumes in a normal female population: application of transvaginal ultrasound.

The volume of residual urine in a normal female population has not been studied and consequently no clear definition of its upper limit exists. Transvaginal ultrasound has been described as a method of identifying and measuring small bladder volumes in the range 2 to 175 ml. This allows the measurement of residual urine volumes without the need for catheterisation. Fifty-three women, who were attending for colposcopic examination agreed to take part in the study. They were deemed normal after denying specific urinary symptoms. Immediately following voiding, transvaginal sonocystography was used to measure residual urine. Forty-five women were found to empty their bladders completely (under 2 ml residual urine). The mean residual volume was 4.8 ml. The upper limit of normal for residual urine volume (taken at the 90th centile) was 10 ml.