CUT-OFF VALUES OF PRESSURE-FLOW STUDY FOR THE DIAGNOSIS OF BLADDER OUTLET OBSTRUCTION IN WOMEN

Introduction: The actual incidence of bladder outlet obstruction in female population is unknown and there are no universally accepted urodynamic criteria for diagnosing female bladder outlet obstruction. This study was designed to define cut-off values of pressure flow study for bladder outlet obstruction in women. Materials and Methods: An urodynamic database of 413 consecutive women was identified. Clinical bladder outlet obstruction was suspected by history and physical examination findings in 39 women. In these patients voiding cystourethrography, pressure-flow study and/or endoscopy were performed to verify the diagnosis. An additional 83 patients presenting for evaluation of stress urinary incontinence served as controls. Three groups of women with bladder outlet obstruction were identified: 19 with urethral stricture (10 who had undergone previous anti-incontinence surgery), 13 with dysfunctional voiding and 7 with high-grade pelvic prolapse. The optimal cut-off values combination of the maximum flow rate (Qmax) and detrusor pressure at maximum flow rate (PdetQmax) for determining obstruction was calculated using receiver operating characteristic (ROC) curves. Sensitivity and specifity were calculated for different cut-off values. Results: The incidence of bladder outlet obstruction was determined to be 9.4% (39/413) in women. The mean age of the obstructed and control groups was 54.0+/-12.9 years and 54.1+/-9.7 years, respectively. In the controls the mean Qmax was 24.8 ml/s, the mean PdetQmax was 27.1 cmH(2)O, the mean post voiding residual urine volume (PVR) was 12.8 ml, the mean detrusor overactivity 26.5%. In the obstructed group the mean Qmax was 10.6 ml/s, the mean PdetQmax was 49.9 cmH(2)O, the mean PVR was 70.3 ml, the mean detrusor overactivity 48.7%. Significant differences were found in the two groups for Qmax (p<0.001), PdetQmax (p<0.001), PVR (p<0.001) and detrusor overactivity (p<0.05). No differences were noted in the two groups for bladder capacity and voided volume. On the basis of receiver operating characteristic curves, using cut-off value the optimal Qmax of 17ml/s or less, sensitivity was 92.3% and specificity was 79.5%. Using cut-off value the optimal PdetQmax of more than 35 cmH(2)O, sensitivity was 82.1% and specificity was 90.4%. Using a combined cut-off value of Qmax of 15 ml/s or less PdetQmax of more than 20 cmH(2)O, sensitivity was 84.6% and specificity was 84.3%. Conclusion: Bladder outlet obstruction in women is seen more frequently than expected. Pressure flow studies are insufficient for definitive diagnosis of bladder outlet obstruction in women in spite of its high rate sensitivity and specificity cut-off values. Clinical findings, endoscopic methods and cut-off values in pressureflow studies should be considered together for the most appropriate diagnostic method.