Discrepancies Between Free and Invasive Uroflowmetry in Women Vary Among Different Clinical Contexts

This study aimed to compare free and invasive uroflowmetry in women with different clinical diagnoses and to evaluate how the discrepancies between both measurements vary by clinical context.

We conducted a retrospective cross-sectional study of 407 women aged ≥18 years who underwent urodynamic studies (UDS) from 2015 to 2021 at an academic hospital in Chile. UDS included free uroflowmetry, cystometry, and pressure-flow studies, following International Continence Society standards. Prior to UDS, patients were classified into five clinical groups: voiding dysfunction (VD), mixed urinary incontinence (MUI), stress urinary incontinence (SUI), overactive bladder-urge incontinence (OAB), and prior anti-incontinence surgery. Maximum flow rates during free uroflowmetry (fQmax) and pressure-flow studies (iQmax) were recorded. ΔQmax (fQmax-iQmax) was analyzed among the different clinical groups and other urodynamic variables using nonparametric tests.

Mean age was 53.9±12 years. Median fQmax was 30 ml/s, significantly higher than iQmax at 17 ml/s; p < 0.001, with a median ΔQmax of 12 ml/s. Correlation between fQmax and iQmax was poor (r = 0.271). ΔQmax varied among groups, being the lowest in VD (5 ml/s; p = 0.004) and the highest in SUI (17 ml/s; p = 0.002). Patients with diabetes also showed a lower ΔQmax (p = 0.001). Patients with urodynamic SUI showed a higher ΔQmax (p = 0.028), while altered cystometric bladder sensation correlated with a lower ΔQmax (p = 0.015).

Differences between free and invasive uroflowmetry vary significantly by diagnosis. SUI patients show the greatest discrepancy, whereas VD and altered sensation result in smaller differences. These findings highlight the need to interpret flow parameters in their clinical context.