EP24.03: Prediction of MBS item number and rASRM stage based on deep endometriosis ultrasound

In March 2022 Australian Medicare Benefits Schedule updated gynecological item numbers relating to endometriosis surgery. Specific item numbers include 35637, 35631 and 35632 (a division of 35638) and 35641 (14). Each item number correlates to staging as per the rAFS (rASRM) stage 1-4, respectively. We aimed to predict to predict four MBS item numbers using ultrasound. A retrospective multicentre study conducted across five countries and six centres from August 2018-November 2019 assessing ultrasound-based rASRM (rASRM-U) correlating with MBS item numbers. This data was also used to evaluate diagnostic accuracy of predicting deep endometriosis following the IDEA consensus with results previously published. Subgroup analysis was performed by dichotomising both ultrasound and surgical stage and MBS item into low and high stage rather than four stage system. 273 patients were included, 54 excluded due to incomplete data. 219 remained for analysis. Prediction of MBS item by rASRM-U stage showed weak agreement with weighted Kappa value 0.31 (0.24 to 0.38, 95% CI). rASRM-U predicted a 0.68 higher surgical stage, alongside large variability with limits of agreement of +/- 1.62 this supports 'over-staging'. Although generally poor for low stage item numbers, there was a sensitivity of 0.96 and specificity 0.44 predicting item 35641. Dichotomised staging shows sensitivity in rASRM-U predicting high stage of 0.99 with specificity 0.34 and NPV 0.95. Prediction of low stage shows sensitivity 0.34, specificity 0.99 and NPV 0.79. The IDEA consensus-based rASRM-U has relatively poor agreement with corresponding MBS item numbers and tends to predict a ‘higher’ stage item. This model is unlikely to predict low stages incorrectly. Although unable to accurately predict individual item numbers for endometriosis surgery, this system was identifies high vs low surgical complexity when ultrasound and surgical groups are dichotomised, and thus could allow for improved surgical planning and financial consent.