BACKGROUND: Clinical, endoscopic, histological, and composite instruments are currently used to measure disease activity in patients with ulcerative colitis (UC). We compared the responsiveness of the Mayo Clinic score (MCS), modified MCS (mMS
excluding physician global assessment), partial MCS (pMS
MCS without endoscopic subscore), Robart's Histopathology Index (RHI), and UC-100 score to change after ustekinumab treatment in patients with moderately to severely active UC. METHODS: Post hoc analysis of the phase 3 UNIFI induction trial (ClinicalTrials.gov: NCT02407236) was conducted. Participants with moderately to severely active UC were randomized to receive ustekinumab or placebo. Treatment assignment was the criterion to assess responsiveness, which was quantified using the probability of a treated participant having a larger change in score than a placebo participant, termed the win probability (WinP), and estimated using nonparametric methods. FINDINGS: The UC-100 score demonstrated large responsiveness (WinP 0.72 [95% confidence interval: 0.66-0.78]), and the MCS (0.68 [0.62-0.73]), mMS (0.69 [0.63-0.75]), and pMS (0.65 [0.59-0.71]) demonstrated similar effect sizes. Of the component items of the Mayo score, the endoscopic subscore (WinP 0.76 [0.69-0.82]) and the stool frequency subscore (WinP 0.74 [0.69-0.79]) were the most responsive. The Inflammatory Bowel Disease Questionnaire (IBDQ) quality-of-life questionnaire was also responsive (WinP 0.78 [0.72-0.82]). CONCLUSIONS: UC disease activity indices are similarly responsive. Depending on the treatment setting, time point of evaluation, and feasibility of measurement, different scores may be used to demonstrate response. These results support the use of mMS as a composite primary endpoint, incorporating both patient-reported and endoscopic outcome measures. The UC-100 score may be more appropriate in settings that also routinely incorporate histological evaluation. FUNDING: There is no funding for this study.