Crohn's Disease Activity Index
Also known as: CDAI
The Crohn's Disease Activity Index (CDAI) is a comprehensive, weighted index for assessing disease activity in Crohn's disease. Developed in 1976 by Best and colleagues for the National Cooperative Crohn's Disease Study, the CDAI integrates eight clinical and laboratory variables into a single score ranging from <150 (remission) to >450 (severe activity). Although more complex than symptom-based tools, the CDAI captures the multidimensional nature of Crohn's disease and remains the reference standard for severe disease assessment.
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When to use it
The CDAI is indicated for baseline severity assessment in newly diagnosed or relapsing Crohn's disease, particularly in patients with severe manifestations, extracolonic complications, or fistulizing disease. It is the preferred tool for clinical trials of induction therapy, regulatory submissions, and documentation of disease severity for prognostic counseling or escalation decisions. The CDAI is less practical for routine office monitoring due to the requirement for 7-day symptom tracking and laboratory values; the Harvey-Bradshaw Index is preferred for frequent office assessments. The CDAI is essential when severity stratification or precise quantification of disease burden is critical.
Strengths & limitations
- Comprehensive capture: Eight variables encompass stool frequency, pain, complications (fistulas, abscesses), hematologic changes, and nutritional status, reflecting the multisystem nature of Crohn's disease.
- Laboratory integration: Incorporates hematocrit and weight, providing objective correlates of disease severity and malabsorption.
- Severity discrimination: Superior ability to distinguish severe disease (CDAI >450) requiring escalation from mild or moderate disease.
- Gold standard in trials: CDAI is mandated by regulatory agencies for efficacy assessment; enables comparison across trials and agents.
- Complexity and burden: Eight variables, including a 7-day diary, make the CDAI cumbersome for routine office use. Compliance with diary-keeping is poor in some populations.
- Laboratory dependency: Requires hematocrit and weight, which may not be available at every visit; delays scoring.
- Antidiarrheal weighting: Scoring penalizes antidiarrheal use (adds 6 points), which may misclassify patients on loperamide for symptom control as having higher disease activity.
- Limited endoscopic correlation: CDAI correlates only moderately (r ~0.4–0.5) with endoscopic severity; patient-reported symptoms may not reflect mucosal inflammation.
Frequently asked
Why does the CDAI have such high weights for pain (20 and 30)?
The weights were derived empirically from the validation study, comparing CDAI scores to steroid response. Pain severity and pain-stool relationship were found to be strong predictors of treatment outcome. However, this emphasis on pain means that psychological factors (e.g., anxiety, irritable bowel syndrome overlap) can inflate CDAI independent of true inflammation. Always correlate CDAI with CRP, ESR, or fecal calprotectin.
Should I use CDAI if the patient cannot keep a 7-day diary?
The full CDAI requires accurate 7-day diary data. If the patient is unwilling or unable to keep a diary, either use the Harvey-Bradshaw Index (HBI) instead, or estimate stool frequency from the patient's recall and note that the CDAI is approximate. For research trials, diary non-compliance is a criterion for exclusion.
How do I interpret CDAI if the patient is on antidiarrheals?
The CDAI penalizes antidiarrheal use by adding 6 points. If a patient is taking loperamide and has a CDAI of 160, the true inflammatory burden may be higher if the antidiarrheal is masking symptoms. Request that the patient temporarily discontinue antidiarrheals for 2–3 days before repeat CDAI measurement, or calculate CDAI both with and without the antidiarrheal component to assess the contribution.
What is the relationship between CDAI and CRP or fecal calprotectin?
CDAI correlates only weakly to moderately (r ~0.3–0.5) with CRP or fecal calprotectin, particularly in mild disease. A patient can have a high CDAI with normal CRP (due to pain or complications) or normal CDAI with elevated CRP (subclinical inflammation). Always use both symptom-based indices (CDAI, HBI) and biomarkers (CRP, fecal calprotectin) for a complete picture.
Is CDAI used for ulcerative colitis?
No. The CDAI was designed specifically for Crohn's disease. For ulcerative colitis, use the Mayo Score, SCCAI, or partial Mayo. The CDAI includes complications (fistulas, abscesses) not applicable to UC.
Sources
- Best, W. R., Becktel, J. M., Singleton, J. W., & Kern, F. (1976). Development of a Crohn's disease activity index. National Cooperative Crohn's Disease Study. Gastroenterology, 70(3), 439–444. DOI: 10.1016/S0016-5085(76)80163-1 ↗
How to cite this page
ScholarGate. (2026, June 3). Crohn's Disease Activity Index. ScholarGate. https://scholargate.app/en/gastroenterology/cdai-crohns
Which method?
Set this method beside its closest kin and read them side by side — the library lays the books on the table; the choice is yours.
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