Postvoid Residual Volume Correlates With Bladder Outlet Obstruction and Not With Detrusor Contraction Strength Parameters in Women: A Matched Case-Control Study.

Purpose: To compare voiding parameters in women with and without increased postvoid residual (PVR) volume, to correlate these parameters with PVR volume and PVR percentage, and to describe their ability to predict an increased PVR volume.

Methods: Retrospective cross-sectional study of urodynamics data prospectively acquired from consecutive symptomatic women over a 5-year period. Patients with spinal cord disorders and with abdominal straining during voiding (abdominal pressure ≥10 cm H2O over baseline at maximum flow rate [Qmax]) were excluded. Increased PVR volume was defined as ≥50 mL. Patients with and without increased PVR volume were matched by age, presence of urodynamic stress urinary incontinence and premicturition bladder volume. Female bladder outlet obstruction (BOO) index (female-BOOI), urethral resistance (UR), projected isovolumetric pressure 1 (PIP1), and relative BOO indexes (female-BOOI/PIP1 and UR/PIP1 ratios) were calculated. Linear regression analysis was applied to correlate the voiding indexes with PVR volume and PVR percentage. The area under the curve (AUC) of the receiver operating characteristic (ROC) analysis was calculated to describe diagnostic accuracy of these indexes for increased PVR volume.

Results: One-hundred ten women with mean age 65.9±13.7 (range, 20-87) years were included. All voiding parameters were significantly different between women with and without increased PVR volume, except for PIP1. Female-BOOI showed the best correlation with increased PVR volume (R2=0.2509, P<0.001) and PVR percentage (R2=0.3677, P<0.001). PIP1 showed no correlation. Relative BOOI indexes did not improve these correlations. ROC curve analyzes confirmed that female-BOOI and UR had good ability to predict increased PVR volume (AUC=0.841 and AUC=0.856, respectively).

Conclusion: PVR volume and PVR percentage correlated with BOO but not to detrusor contraction strength parameters in symptomatic women that void without abdominal straining. The results of this study contribute to the understanding of the pathophysiology of increased PVR volume in women.