Urodynamic investigation remains the gold standard for assessment of lower urinary tract function in women. Despite its widespread use, urodynamics (UDS) is an invasive test which can be uncomfortable for patients and incur additional cost and time [1]. A common application of UDS is to investigate refractory overactive bladder symptoms (OAB) with the aim to observe detrusor overactivity (DO). Ultrasound (US) measurement of bladder wall thickness (BWT) has been previously proposed as an alternative method for identifying DO [2, 3].
We hypothesise that US measurement of BWT is an accurate method for diagnosing DO.

This review was registered on PROSPERO and the PRISMA guidelines were followed throughout. A literature search was conducted of databases: “Embase”, “Medline”, “PubMed”, “Google Scholar”, and “Open Access Thesis and Dissertation”. Two independent reviewers screened abstracts for inclusion (see figure 1 and table 1). A risk of bias assessment was conducted using Robins-I V2 tool. Meta-analysis was conducted with exclusion of one study to reduce data heterogeneity. Statistical analysis was conducted using IBM SPSS Statistics.

225 abstracts were screened with 9 studies being included in our final review and analysis (see figure 1 and 2). 8 studies measured BWT using a transvaginal approach and 1 used transabdominal scanning. 7 studies performed lab UDS and 2 utilised ambulatory UDS +/- video-cystourethrography for diagnosing DO. 5 studies concluded that BWT measurement can be used to diagnose DO suggesting a diagnostic threshold of approximately 5mm (4.4mm-5mm). Studies looking a 5mm BWT for diagnosis of DO reported sensitivities 43-84% and specificities 62-89%. 
Paired samples T-test was performed. The mean BWT in those “with DO” was found to be 5.234 +/- 1.424 and those “without DO” 4.356+/-1.124. Those “with DO” were found to have a mean increased BWT of 0.879 +/-0.958 (95% CI 0.143 to 1.615) when compared to those “without DO”. This was found to be a statistically significant difference t=2.754, p=0.025, d=0.958.
Meta-analysis was performed from six studies (possible from the data published) where transvaginal US measurement of BWT was used. The overall effect size was 0.196 with confidence intervals crossing the no effect value (see figure 3).

The mean difference between BWT measured in those “with DO” and those “without DO” is statistically different. However, the spread of measurements taken is broad meaning that variance and confidence intervals about this mean are large (i.e. the distribution of data is wide and flat about the mean) and effect size crosses the no effect value (see figure 3). This means that ultrasound measurement of BWT is ineffective for diagnosis of DO and this approach cannot be used to replace urodynamics.

There is variation in US method for measuring BWT and UDS technique used in studies included in this review. Different diagnostic thresholds have been proposed for determining DO, however, current literature does not indicate that BWT measurement can reliably identify DO.

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