Early Identification of Patients with Steroid Non-Response in Acute Severe Ulcerative Colitis: External Validation of the ASUC Score and Comparison with Established Prognostic Models

Background/Objectives: Acute severe ulcerative colitis (ASUC) affects up to one quarter of patients with ulcerative colitis and carries a substantial risk of colectomy. Early recognition of the need for escalation beyond intravenous (IV) corticosteroids is essential, yet most indices—such as the Oxford criteria—require reassessment on day 3, delaying rescue therapy. The ASUC score, based on admission albumin, C-reactive protein (CRP), endoscopic severity (Ulcerative Colitis Endoscopic Index of Severity, UCEIS), and pre-admission steroid use, was recently proposed to predict early escalation at admission. This study aimed to externally validate the ASUC score and compare its performance with established indices. Methods: We performed a single-center retrospective validation study including consecutive ASUC admissions (2015–2024). The primary outcome was escalation beyond IV steroids, defined as medical rescue therapy with infliximab or ciclosporin and/or colectomy during the index hospitalization. As a sensitivity analysis providing a more specific estimate of IV corticosteroid non-response, we repeated analyses restricting the outcome to medical rescue therapy alone. The model performance was assessed for discrimination (AUC and bootstrap-corrected 2000 resamples), calibration (intercept, slope, and Brier score), and clinical utility (decision-curve analysis). Comparator indices included Albumin-CRP-Endoscopy score (ACE), Admission Model for Acute Severe Colitis (ADMIT-ASC), Oxford Day 3, Lindgren, and Edinburgh. Predefined subgroup analyses (exploratory and underpowered) evaluated infection and biologic exposure. Results: Ninety-one admissions were included overall. The primary validation was performed in the infection-free cohort (n = 77), and infected cases (n = 14) were analyzed separately. In the infection-free cohort, 17/77 (22.1%) required escalation beyond IV steroids during the index hospitalization (medical rescue therapy and/or colectomy), and 5/91 (5.5%) underwent colectomy within 90 days. The ASUC score showed excellent discrimination (Area under the receiver-operating characteristic curve [AUC] 0.89, 95% Confidence Interval [CI] 0.81–0.95), good calibration (intercept 0.26, slope 1.29), and net clinical benefit across 30–50% thresholds. In the rescue-only sensitivity analysis, discrimination remained high (AUC 0.86, 95% CI 0.77–0.94). At a cut-off of ≥2, sensitivity 94% and specificity 78% outperformed other indices (AUC 0.62–0.83). Exploratory subgroup analyses were imprecise due to small sample sizes; discrimination was lower in the infected-only subgroup (AUC 0.71), and estimates in biologic-experienced patients were unstable because of severe imbalance. Conclusions: The ASUC score accurately identified patients likely to require escalation beyond IV steroids on the day of admission, outperforming or matching established day-3 indices. Its simplicity and reliability support its integration into early ASUC management to expedite rescue therapy and potentially improve outcomes.