Bladder outlet obstruction index and maximal flow rate during urodynamic study as powerful predictors for the detection of urodynamic obstruction in women

Aims: To evaluate whether bladder outlet obstruction index (BOOI), a mathematical index of outlet resistance, in association with maximal flow rate (Qmax) obtained during multichannel urodynamics (UDS) or detrusor pressure at maximal flow rate (PdetQmax) could help the identification of obstruction in women. Methods: From January 2004 to February 2005, 401 women were assessed in our urodynamic unit. Of these, 133 were neurologically intact women, referred symptoms suggestive of voiding disorders and had an abnormal non-intubated uroflussometry (NIF) (BOO group). A normal NIF was defined as a bell-shaped curve in presence of a Qmax >15 ml/sec and a PVR <50 ml. Symptoms of voiding disorders were ascertained by interview and rated positive if they occurred more than occasionally. Thirty-seven women were enrolled as unobstructed if they presented a normal NIF and symptoms suggestive of voiding disorders less than occasionally (unobstructed group). Results: ROC curve demonstrated similar diagnostic accuracy in the diagnosis of urodynamic obstruction for Qmax obtained during UDS (AUC = 0.908; P < 0.0001; CI99% = 0.831 to 0.985) and BOOI (AUC = 0.879; P < 0.0001; CI99% = 0.794 to 0.918) and the least was seen for PdetQmax (AUC = 0.706; P = 0.001; CI99% = 0.620 to 0.830). A Qmax obtained during UDS cut-off ?15 ml/sec provides specificity of 85.9% and sensitivity of 78.9%. A BOOI cut-off ?-8 provides a sensitivity of 80.8% and specificity of 86.1%. The weakest sensitivity (64.2%) and specificity (64.6%) was recorded for PdetQmax ?28 cmH2O. Conclusions: BOOI and Qmax obtained during UDS appears to be the most discriminating urodynamic parameters of female BOO. The use of these cutoff might facilitate the identification of women with functional and anatomical obstruction.