Prediction of MBS item codes for endometriosis surgery using transvaginal ultrasound

Background and Aims: In March 2022, updates in the Australian Medicare Benefits Schedule relating to endometriosis surgery were made relating to item numbers 35637, 35631 and 35632 (division of 35638) and 35641. Updated codes aligned with rASRM Stages 1, 2, 3 and 4 endometriosis respectively. This study aims to assess an IDEA consensus-based ultrasound rASRM predicting MBS item. Materials and Methods: Retrospective multicentre study conducted across five countries and six centres. Data collection from August 2018 to November 2019 assessing ultrasound staged rASRM (rASRM-U). Subgroup analysis was performed, dichotomizing rASRM-U and MBS items into low and high stages. Results: 273 patients were included, 54 excluded due to incomplete data. 219 remained for analysis. Predicting MBS item by rASRM-U stage showed weak agreement with a weighted Kappa value of 0.31 (0.24 to 0.38, 95% CI). rASRM-U predicted a 0.68 higher surgical stage supporting ‘over-staging’. Although generally poor for low-stage item numbers, there was a sensitivity of 0.96 and specificity of 0.44 predicting item 35641. Dichotomised staging shows sensitivity in rASRM-U predicting high-stage of 0.99 with specificity of 0.34 and NPV of 0.95. Prediction of low-stage shows sensitivity of 0.34, specificity of 0.99, and NPV of 0.79. Conclusion: The IDEA consensus-based rASRM-U has relatively poor agreement with corresponding MBS item numbers, tending to predict ‘higher’ stages. This model is unlikely to predict low stages incorrectly. Although unable to accurately predict individual item numbers for endometriosis surgery, this system identifies high versus low surgical complexity when ultrasound and surgical groups are dichotomized; thus, it could allow improved surgical and financial planning.