Developing and Validating a New Nomogram for Diagnosing Bladder Outlet Obstruction in Women

Objective: To develop and validate a nomogram for assessing bladder outlet obstruction (BOO) in women derived from concurrent P and Q based on radiographic evidence of increased urethral resistance.

Patients And Methods: Retrospective analysis of prospectively acquired video-urodynamics and clinical data of 185 women (development cohort) was performed. The P were plotted against Q and cluster analysis was performed to determine an axis that best divided the definitively obstructed and unobstructed. Using data from a further 350 women (validation cohort), the sensitivity and specificity of the derived criterion was calculated. Finally, the data from both groups was pooled together and using binary logistic regression analysis, a nomogram was produced.

Results: Of the 535 patients in the two cohorts, (122 [22.8%]) demonstrated radiographic evidence of BOO. Cluster analysis identified the axis that best separates the radiographically obstructed and unobstructed as P  = 2*Q . Using the data from the validation cohort, the sensitivity and specificity for this was calculated as 0.94 and 0.93, respectively. A nomogram, representing the probability of BOO for concurrent P and Q measurements was derived by pooling data from both cohorts. Alternatively, a female BOO index (BOOIf) may be calculated mathematically using the formula BOOIf = P  - 2.2*Q BOOIf < 0, <10% probability of obstruction, BOOIf > 5 likely obstructed (50%) and If BOOIf > 18, obstruction almost certain (>90%).

Conclusion: A female BOO nomogram (the SG nomogram) with high sensitivity and specificity is proposed. The nomogram can be used to stratify the degree of BOO or assess response to treatment.