Introduction and hypothesis: Mixed urinary incontinence (UI) is, on average, more severe than urgency UI or stress UI. We tested the hypothesis that mixed UI is a more advanced stage of UI by comparing transition probabilities among women with stress, urgency, and mixed UI.
Methods: We used data from the General Longitudinal Overactive Bladder Evaluation Study-UI, which included community-dwelling women, aged 40+ years, with UI at baseline. Study participants completed two or more consecutive bladder health surveys every 6 months for up to 4 years. Using sequential 6-month surveys, transition probabilities among UI subtypes were estimated using the Cox-proportional hazards model, with the expectation that probabilities from stress or urgency UI to mixed UI would be substantially greater than probabilities in the reverse direction.
Results: Among 6,993 women 40+ years of age at baseline, the number (prevalence) of women with stress, urgency, and mixed UI was 481 (6.9%), 557 (8.0%), and 1488 (21.3%) respectively. Over a 4-year period, the transition probabilities from stress UI (34%) and urgency UI (27%) to mixed UI was significantly higher than probabilities from mixed to stress UI (6%) or to urgency UI (rate = 9%). The adjusted transition hazard ratio for stress UI and urgency UI was 2.06 (95% CI: 1.73-2.92) and 1.85 (95% CI: 1.63-2.57) respectively compared with mixed UI.
Conclusion: The substantially higher transition from stress UI and urgency UI to mixed UI supports the hypothesis that mixed UI might represent a more advanced stage of UI that may have implications for understanding disease progression.
Keywords: Epidemiology; Mixed urinary incontinence; Progression; Stress urinary incontinence; Transition; Urgency urinary incontinence.