Determination of postvoid residual by translabial ultrasound

Urogynaecological assessment routinely includes determination of postvoid residual urine volume (PVR). This study was designed to generate a formula for determining PVR by translabial ultrasound (US). This was an observational study using imaging data obtained during urodynamic testing between July 2009 and November 2010. Bladder dimensions were determined by translabial US (midsagittal plane) and blinded against PVR on catheterisation. The relationship between PVR and bladder dimensions was modelled using linear regression. Predictive performance was quantified using Pearson's correlation and R (2) statistic. In 207 individuals, 243 PVRs were obtained by catheterisation (0-650 ml). An optimal regression model comprised the product of height and depth US measurements and a coefficient of 5.59 [95 % confidence interval (CI): 5.41-5.76, p < 0.0001)] This regression equation yielded an R (2) = 0.94; Pearson's correlation was 0.97. Translabial US is a convenient and accurate method for measuring PVR. We propose the formula height x depth x 5.6 = postvoid residual in millilitres.