Testing Accuracy of Voiding Function Tests During Complex Urodynamic Study

Objectives: Urodynamic study (UDS) evaluates voiding function through two different methods: free uroflowmetry and pressure flow study (PFS). There is wide variability for both voiding assessment methods. While PFS is essential in the assessment of male bladder outlet obstruction, its use in women is debated. It may be helpful to use both for final decision making on voiding function in women. Our objective is to evaluate the relationship between these two methods using correlation analysis and diagnostic accuracy testing.

Methods: We conducted a retrospective chart review of women aged >18 years who underwent UDS from January 1, 2019, to December 31, 2022, at a University Hospital System. After chart review, 169 consecutive women met the criteria to be included in the study analysis. Data were extracted through manual chart review. If the recorded voided volume was below 150 cc for either free uroflowmetry or PFS, the patient was excluded. Standard UDS started with free uroflowmetry, followed by filling cystometry and ended with PFS. A Qm > 20 mL/sec was considered consistent with adequate flow.

Results: Baseline demographics are listed in Table 1. When comparing free uroflowmetry and PFS, there was a weak Pearson correlation (r) for the maximum flow (Qm): r = 0.40 (p < 0.0001) and average flow (Qa): r = 0.25 (p = 0.0015). When PFS is used as the gold standard, the sensitivity of free uroflowmetry was 0.80 ± 0.04 and specificity was 0.25 ± 0.05 for detecting adequate voiding. Free uroflowmetry and PFS were consistent in detecting adequate flow in 49% of patients (n=83). Free uroflowmetry found adequate flow while PFS showed inadequate flow in 29% of patients (n=49). Lastly, free uroflowmetry found inadequate flow while PFS showed adequate flow in 9% of patients (n=16). When both test results were combined for assessment of voiding function, 88% patients were found to have adequate voiding.

Conclusions: It is evident that there exists a weak correlation between free uroflowmetry and PFS with respect to Qm and Qa. Performing both tests will increase success in confirming adequate flow in patients. Considering these values and a lower specificity, one could consider additional testing with PFS if free uroflowmetry is inadequate, but PFS may not always be indicated.