Abstract Background Intestinal ultrasound (IUS) is a validated, non-invasive imaging modality for assessing disease activity in ulcerative colitis (UC). Its role in acute severe ulcerative colitis (ASUC) remains under evaluation. This systematic review and expert consen-sus were initiated by the International Bowel Ultrasound Group (IBUS) and aimed to define the role of IUS in ASUC, including comparison with other imaging modalities and endoscopy. Methods A systematic review and expert consensus were conducted using a Delphi process on the use of IUS in the clinical assessment of in adult and pediatric ASUC. 1253 studies were found in Scopus, Cochrane, Web of Science, and PubMed. 868 studies were screened, 47 were selected for full text review and 34 were included in the analysis. Statements were formulated on the diagnostic, monitoring, and prognostic roles of IUS in ASUC and level of evidence (EL) was classified according to GRADE (Grading of Recommenda-tions Assessment, Development, and Evaluation) approach. Two online rounds of voting were completed along with iterative statement refinement. Consensus was de-fined as 80% agreement voted as “agree” or “strongly agree.” Results 19 out of 24 statements had agreement ( 80%) in the first voting round, and 4 of 6 statements did in the second voting round. IUS demonstrated value as an alternative to computed tomography (CT) for assessing treatment response and disease activity in patients with acute severe ulcerative colitis, though it is not recommended for excluding complications such as perforation (EL Moderate, 89% agreement). In such cases, abdominal X-ray or CT remains the preferred imaging modality (EL Low, 87% agreement). IUS was also found useful for monitoring disease progression in ASUC, particularly when endoscopy is contraindicated or poses procedural risks (EL Moderate, 95% agreement). To optimize disease monitoring and therapeutic assessment, IUS should be performed at baseline and may be repeated as early as 48 hours after treatment initiation, followed by evaluations at 2 weeks, 4 - 6 weeks, and 8 - 12 weeks (EL Moderate, 87% agreement). These findings support a structured approach to incorporating IUS in the management and follow-up of ASUC, complementing traditional imaging and endoscopic assessments. Conclusion While endoscopy remains essential for baseline diagnosis, severity assessment, and CMV diagnostics, IUS provides a reliable, non-invasive, and dynamic assessment of ASUC activity and treatment response. It complements endoscopy, reduces procedural burden, and enables early treatment optimization. Integration of IUS into ASUC algorithms is supported by current evidence and expert consensus. Conflict of interest: Lu, Cathy: Advisory board - Abbvie, Johnson and Johnson, Takeda, Ferring, Merck, Celltrion, Lilly, Pfizer, Pendopharm, Agomab. Research Funding - Abbvie, Helmsley Charitable Trust, Alberta Innovates Verstockt, Bram: - Research support from AbbVie, Biora Therapeutics, Celltrion, Landos, Pfizer, Sanofi, Sossei Heptares/Nxera and Takeda. - Speaker’s fees from Abbvie, Agomab, Alfasigma, Biogen, Bristol Myers Squibb, Celltrion, Eli Lily, Falk, Ferring, Galapagos, Materia Prima, Johnson and Johnson, Pfizer, Sandoz, Takeda, Tillots Pharma, Truvion and Viatris. - Consultancy fees from Abbvie, Alfasigma, Alimentiv, Anaptys Bio, Applied Strategic, Astrazeneca, Atheneum, BenevolentAI, Biora Therapeutics, Boxer Capital, Bristol Myers Squibb, Domain Therapeutics, Eli Lily, Galapagos, Guidepont, Landos, Merck, Mirador Therapeutics, Mylan, Nxera, Inotrem, Ipsos, Johnson and Johnson, Pfizer, Sandoz, Sanofi, Santa Ana Bio, Sapphire Therapeutics, Sosei Heptares, Takeda, Tillots Pharma and Viatris. - Stock options Vagustim and Thethis Pharma. Allocca, Mariangela: Personal Fees: consulting fees from Nikkiso Europe, Mundipharma, Janssen, Abbvie, Pfizer, Ferring, Galapagos, Sandoz, Lilly and Alfasigma de Voogd, Floris: Personal Fees: Speaker and/or honoraria fees from AbbVie, Galapagos, Janssen, Pfizer and Takeda Fraquelli, Mirella: No conflict of interest Sagami, Shintaro: Shintaro Sagami has served as an advisory board member, consultant, or speaker for AbbVie, Alimentiv, Bristol Myers Squibb, Celltrion, EA Pharma, Eli Lilly, Ferring Pharmaceuticals, Gilead Sciences, Janssen Pharmaceuticals, Kyorin Pharmaceutical, Mitsubishi Tanabe Pharma, Mochida Pharmaceutical, Nippon Kayaku, Pfizer, Takeda, and Zeria Pharmaceutical, and has received research funding from Bristol Myers Squibb, EA Pharma, Gilead Sciences, Helmsley Charitable Trust, JIMRO, Kyorin Pharmaceutical, Miyarisan, Mochida Pharmaceutical, Nippon Kayaku, Pfizer, Sekisui Medical, Samsung, Takeda, and Zeria Pharmaceutical. Blunt, Heather: No conflict of interest Vitale, Elaina: No conflict of interest Bravo, Catarina: No conflict of interest Gu, Phillip: No conflict of interest Hudson, Alexandra: No conflict of interest O’brien, Maureen: No conflict of interest Pruijt, Maarten: No conflict of interest Kakkadasam Ramaswamy, Pradeep: No conflict of interest Seidelin, Jakob Benedict: J.B.S. has received research grants from Takeda, Janssen, the Danish Research Council, and the Capital Region Denmark, and is the national coordinator of studies from AbbVie, Arena Pharmaceuticals, Ely Lilly, and Boehringer Ingelheim.
Lu et al. (Thu,) studied this question.