Assessing Crohn's disease activity for clinical trial enrolment and endpoint reporting.
Evaluating therapeutic response to biologics and immunomodulators in clinical practice.
Classifying disease as remission, mild, moderate, or severe for treatment planning.
Historical FDA regulatory endpoint — most Crohn's trials from 1976–2020 used CDAI-based endpoints.
Clinical Context
CDAI requires a 7-day patient diary. The Harvey-Bradshaw Index (HBI) is preferred at point of care as a validated same-day surrogate (r = 0.93 with CDAI).
Requires 7-day diary — impractical in urgent settings; use HBI at bedside.
No endoscopic component — CDAI remission does not correlate reliably with mucosal healing.
Body weight and haematocrit components can be affected by non-inflammatory factors.
Post-2020 trials increasingly favour PRO-2 (patient-reported stool frequency + pain) or SES-CD + HBI combined.
CDAI ↔ HBI Conversion
CDAI ≈ 68.9 + (43.9 × HBI) — validated regression equation (Harvey & Bradshaw 1980; r = 0.93). Use for cross-referencing historical trial data.
Section 4
Next Steps
Clinical Actions
01
CDAI < 150 (Remission): Maintain therapy; set surveillance endoscopy (mucosal healing confirmation); ensure adequate bone density monitoring.
02
CDAI 150–219 (Mild): Optimise 5-ASA, antibiotics, or budesonide; check faecal calprotectin and CRP.
03
CDAI 220–449 (Moderate): Systemic steroids or biologic initiation; GI specialist review; exclude infection first.
04
CDAI ≥ 450 (Severe): Hospitalise; IV steroids or IV biologic; surgical IBD team; treat complications (abscess, obstruction).
Section 5
Evidence Appraisal
Primary Reference
Development of a Crohn's disease activity index. National Cooperative Crohn's Disease Study
Best WR et al. • Gastroenterology. 1976;70(3): 439–444
Section 6
Literature
Development History
Developed in 1976 by William Best and colleagues as part of the National Cooperative Crohn's Disease Study (NCCDS) — the first large US multicentre randomised controlled trial in Crohn's disease. The index was designed to quantify disease activity objectively for trial purposes across 569 patients at 14 participating institutions.
Regulatory Legacy
The FDA adopted CDAI-based endpoints (remission = CDAI < 150; response = CDAI reduction ≥ 100) as the standard for Crohn's disease biologic licensing trials from the late 1990s through to the 2010s. The PRO-2 (stool frequency + abdominal pain) has now been endorsed by the FDA and EMA as a more patient-centred alternative trial endpoint.
