Diagnostic test accuracy of each of the four <scp>IDEA</scp> ultrasound steps in predicting presence of deep endometriosis

OBJECTIVE: To determine the diagnostic performance of each additional step of the four-step International Deep Endometriosis Analysis (IDEA) consensus protocol for predicting the presence of deep endometriosis (DE) on transvaginal ultrasound. METHODS: This was an international multicenter observational cohort study of data collected prospectively between August 2018 and November 2019, with analysis performed retrospectively. Individuals with symptoms and/or signs suggestive of endometriosis were recruited from tertiary gynecological services, underwent pelvic transvaginal ultrasound assessment according to the IDEA consensus protocol and underwent laparoscopy for excision of endometriosis. Sensitivity, specificity, accuracy, positive (PPV) and negative (NPV) predictive values, and positive (LR+) and negative (LR-) likelihood ratios for individual and cumulative steps of the IDEA protocol in diagnosing DE were calculated with corresponding 95% CIs. Visual diagnosis at laparoscopy was used as the reference standard. RESULTS: In total, 640 participants were recruited, of whom 467 were included in the analysis. With the addition of each step of the four-step IDEA consensus protocol, the cumulative sensitivity for diagnosing DE increased progressively, from 0.65 (95% CI, 0.59-0.71) for Step 1 only to 0.94 (95% CI, 0.90-0.97) for Steps 1-4, the specificity decreased from 0.78 (95% CI, 0.72-0.84) to 0.58 (95% CI, 0.52-0.65), the accuracy increased from 0.71 (95% CI, 0.67-0.75) to 0.78 (95% CI, 0.74-0.81), PPV decreased from 0.78 (95% CI, 0.73-0.82) to 0.73 (95% CI, 0.70-0.76), NPV increased from 0.65 (95% CI, 0.61-0.69) to 0.89 (95% CI, 0.83-0.92), LR+ decreased from 3.02 (95% CI, 2.30-3.69) to 2.27 (95% CI, 1.93-2.67) and LR- decreased from 0.44 (95% CI, 0.37-0.53) to 0.10 (95% CI, 0.06-0.17). CONCLUSIONS: This validation study supports the use of the comprehensive four-step IDEA consensus protocol in detecting DE and justifies referral for specialist imaging in cases of suspected endometriosis. © 2026 The Author(s). Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.