A mixed methods study to assess the feasibility of a randomised controlled trial of invasive urodynamic testing versus clinical assessment and non-invasive tests prior to surgery for stress urinary incontinence in women: the INVESTIGATE-I study

Background The position of invasive urodynamic testing (IUT) in diagnostic pathways for urinary incontinence is unclear, and systematic reviews have called for further trials evaluating clinical utility. The objective of this study was to inform the decision whether to proceed to a definitive randomised trial of IUT compared to clinical assessment with non-invasive tests, prior to surgery in women with stress urinary incontinence (SUI) or stress-predominant mixed urinary incontinence (MUI).

Methods A mixed methods study comprising a pragmatic multicentre randomised pilot trial, a qualitative face-to face interview study with patients eligible for the trial, an exploratory economic evaluation including value of information study, a survey of clinicians’ views about IUT, and qualitative telephone interviews with purposively sampled survey respondents. Only the first and second of these elements are reported here.

Trial participants were randomised to either clinical assessment with non-invasive tests (control arm) or clinical assessment with non-invasive tests plus IUT (intervention arm).

The main outcome measures of these feasibility studies were confirmation that units can identify and recruit eligible women, acceptability of investigation strategies and data collection tools, and acquisition of outcome data to determine the sample size for a definitive trial. The primary outcome proposed for a definitive trial was ICIQ-FLUTS (total score) 6 months after surgery or the start of nonsurgical treatment.

Results Of 284 eligible women, 222 (78 %) were recruited, 165/219 (75 %) returned questionnaires at baseline, and 125/200 returned them (63 %) at follow-up. Most women underwent surgery; management plans were changed in 19 (19 %) participants following IUT.

Participants interviewed were positive about the trial and the associated documentation.

Conclusions All elements of a definitive trial were rehearsed. Such a trial would require between 232 and 922 participants, depending on the target difference in the primary outcome. We identified possible modifications to our protocol for application in a definitive trial including clarity over inclusion/exclusions, screening processes, reduction in secondary outcomes, and modification to patient questionnaire booklets and bladder diaries. A definitive trial of IUT versus clinical assessment prior to surgery for SUI or stress predominant MUI is feasible and remains relevant.

Trial registration Current Controlled Trials: ISRCTN71327395, registered 7 June 2010.