Calculate the CDAI score from 8 weighted clinical variables. Includes component breakdown, activity classification, and common clinical-trial thresholds.
The Crohn's Disease Activity Index (CDAI), developed by Best, Becktel, Singleton, and Kern in 1976, is the classic composite index used in Crohn's disease clinical trials. It integrates eight clinical variables — liquid stools, abdominal pain, general well-being, extra-intestinal complications, anti-diarrheal use, abdominal mass, hematocrit, and body weight — collected over a 7-day diary period into a single composite score.
CDAI scores below 150 define clinical remission, 150-219 indicate mildly active disease, 220-450 represent moderately active disease (the typical clinical trial enrollment range), and scores above 450 indicate severely active disease. The CR-100 (≥100 point decrease) and CR-70 (≥70 point decrease) are standard response endpoints used in pivotal drug approval trials.
This calculator computes all 8 weighted CDAI components, provides a detailed percentage breakdown showing which variables drive the score, classifies disease activity, and maps scores to common clinical-trial thresholds. It is best used as a structured scoring worksheet rather than as a stand-alone treatment rule.
The CDAI is still the standard way to summarize Crohn's disease activity from the symptom diary, abdominal findings, hematocrit, and weight change. This calculator keeps the weighted components, activity bands, and trial thresholds together so the score can be reviewed without recreating the spreadsheet logic by hand.
CDAI = (stools × 2) + (pain × 5) + (well-being × 7) + (features × 20) + (lomotil × 30) + (mass × 10) + (Hct deviation × 6) + (weight% deviation × 1) Hct deviation = normal − actual (male normal: 47%, female: 42%) Weight deviation = [1 − (current/ideal)] × 100
Result: CDAI = 84 + 60 + 98 + 20 + 0 + 0 + 24 + 8.3 = 294. Moderately active disease.
A patient averaging 6 stools/day, moderate pain, and poor well-being has a CDAI of 294 — moderately active disease in the range often used for clinical-trial enrollment (220-450). The page is summarizing the score and usual trial bands, not prescribing a specific therapy.
The CDAI was developed in 1976 by William Best and colleagues at the Midwest Regional Health Center through a National Cooperative Crohn's Disease Study. They analyzed 18 candidate variables in 187 patient visits and used multiple regression to identify the 8 most predictive variables and their optimal weights. The resulting index has been used in virtually every Crohn's disease clinical trial since, including the landmark studies that led to approval of infliximab, adalimumab, vedolizumab, ustekinumab, and risankizumab.
While the CDAI remains an accepted primary endpoint, the field is moving toward treat-to-target strategies using objective endpoints. The STRIDE-II consensus (2021) recommends targeting both clinical remission (PRO2: stool frequency ≤1.5/day + abdominal pain ≤1) AND endoscopic remission (SES-CD ≤ 2 or absence of ulcers). Biomarkers including CRP normalization and fecal calprotectin < 150 µg/g serve as intermediate targets.
For Crohn's patients with refractory disease, CDAI > 300-350 despite optimized medical therapy is one factor supporting surgical discussion. However, surgical decisions are made in conjunction with imaging (MR enterography, CT), endoscopy, nutritional status, and patient preferences. The CDAI alone should not drive surgical timing.
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This worksheet follows the original eight-variable CDAI structure. It adds the seven-day totals for stool frequency, abdominal pain, and general well-being, then applies the published weights for extra-intestinal features, anti-diarrheal use, abdominal mass, hematocrit deviation, and percent deviation from ideal body weight. The page then maps the total score to the usual remission, mild, moderate, and severe activity bands used in trial reporting.
The result is a scoring aid, not a substitute for current endoscopic, biomarker, imaging, and clinician review. Modern Crohn's assessment often pairs symptom scores with objective inflammation measures such as CRP, fecal calprotectin, and endoscopic findings.
Crohn's disease symptoms fluctuate day-to-day. The 7-day diary captures this variability more reliably than a single-point assessment. Clinical trials require at least 7 days of diary data before screening and endpoint visits. For clinical practice, a 7-day recall period is often used as a pragmatic alternative to daily diaries.
CR-70 (Clinical Response-70) requires a ≥70 point decrease from baseline CDAI. CR-100 requires a ≥100 point decrease. CR-100 is the more stringent endpoint used in most pivotal trials. Some newer trials use CR-70 as an early response marker. Both require the patient to start above CDAI 220.
Yes, though it's being supplemented. The FDA still accepts CDAI as a co-primary endpoint. However, newer trials increasingly use patient-reported outcome (PRO) components (stool frequency + abdominal pain, called CDAI-PRO2), and endoscopic endpoints (SES-CD, Rutgeerts score). The trend is toward composite endpoints combining symptoms with objective mucosal healing.
The CDAI relies heavily on subjective symptoms and does not correlate well with endoscopic inflammation. Patients can have high CDAI from irritable bowel-like symptoms without active inflammation, or low CDAI despite endoscopic ulceration. It does not capture fistulizing disease well. The hematocrit and weight components are less specific than inflammatory markers like CRP and fecal calprotectin.
The Harvey-Bradshaw Index (HBI) is a simplified version using just 5 variables without requiring 7-day diaries: well-being, abdominal pain, liquid stools (1 day), abdominal mass, and complications. HBI < 5 ≈ remission, 5-7 ≈ mild, 8-16 ≈ moderate, > 16 ≈ severe. HBI correlates well with CDAI (r ≈ 0.93) and is preferred in clinical practice for its simplicity.
The CDAI counts 7 extra-intestinal complications, each adding 20 points: arthritis/arthralgia, iritis/uveitis, erythema nodosum, pyoderma gangrenosum, aphthous ulcers (oral), anal fissure/fistula/abscess, and fever >100°F (37.8°C). These are counted as present/absent during the assessment week.