RHI remission (< 6) is a key endpoint in many Phase 3 UC trials. It is more stringent than earlier indices like the Geboes score.
Guidelines & Evidence
Clinical Details
Section 1
When to Use
When to Use
Standardized scoring of mucosal healing in Ulcerative Colitis (UC) clinical trials
To quantify histological response following induction or maintenance of biologics (e.g., Infliximab)
Measuring deep mucosal healing beyond macroscopic endoscopic visibility
Clinical Target
The RHI is a validated histological tool that correlates with clinical outcomes and provides better inter-observer consistency than older subjective indices.
RHI was developed using rigorous "Operating Characteristic" analysis to identify which histological features actually predicted clinical response. By weighting "Erosions" and "Epithelial Neutrophils" more heavily (factor of 5 and 3), the index accurately reflects the markers most correlated with imminent relapse.
Histological Remission (RHI ≤ 6)
Achieving an RHI of ≤ 6 (with subscores of 0 for neutrophils and ulcers) is the ultimate goal of "Deep Remission." Patients at this level have significantly lower rates of colonic dysplasia and surgery compared to those in clinical-only remission.
Clinical Pearls
Inter-observer reliability is high (weighted Kappa > 0.75), making it suitable for multi-center global trials
The presence of neutrophils in the surface epithelium is considered more significant than in the deep crypts
RHI is often used alongside the Mayo Endoscopic Subscore (MES) to provide a 360-degree view of healing
Section 4
Next Steps
Management Action
01
RHI < 6: Target achieved; continue current maintenance.
02
RHI > 12: Active histological disease. If biomarkers (Calpro) are also high, consider therapeutic escalation.
Complementary Scoring
Nancy Histological Index (Simplified Alternative)
Geboes Score (Original Standard)
Mayo Endoscopic Score
Section 5
Evidence Appraisal
The Defining Scale
Development and validation of a histological index for UC.
Mosli MH et al. • Gut. 2017;66(1):50-58. The foundational study establishing the RHI weighting and validation.
Developed by the Robarts Research Institute in London, Ontario, Canada. The institute is a world-renowned clinical trials center led by IBD pioneers like Brian Feagan. The RHI was created specifically to meet the high statistical demands of modern drug licensing agents (FDA/EMA).
