Crohn's Disease Activity Index Calculator

Crohn's Disease Activity Index Calculator for Gastroenterology. Scores of 150 or below indicate clinical remission (quiescent disease); above 150 indicates active disease. Trials commonly stratify as mild-to-moderate (roughly 150-220), moderate-to-severe (about 220-450), and severe/fulminant (above 450). A drop of 70 points (CDAI-70) is a conventional clinical response threshold and 100 points (CDAI-100) a more stringent one; remission is a score under 150. These bands drive trial eligibility and endpoint adjudication, but in practice the CDAI correlates poorly with mucosal inflammation, so a low score does not confirm endoscopic or biochemical healing.

How this calculator works

The CDAI is a weighted composite score derived by multiple regression against physicians' global assessments in the National Cooperative Crohn's Disease Study. Eight variables are each multiplied by a fixed coefficient and summed: liquid/soft stools over 7 days (x2), abdominal pain rated 0-3 daily and summed over 7 days (x5), general wellbeing rated 0-4 daily and summed over 7 days (x7), number of extraintestinal complications and findings (arthralgia, uveitis, erythema nodosum/pyoderma/aphthae, anal fissure/fistula/abscess, other fistula, fever) (x20), use of antidiarrheals (x30), abdominal mass (0/2/5, x10), the difference of 47 minus hematocrit adjusted for sex (x6), and percentage deviation of body weight from standard (x1). Scores typically range from about 0 to 600.

When to use this calculator

The CDAI is the historical reference endpoint for measuring symptomatic disease activity in adults with luminal (small bowel and/or colonic) Crohn's disease, used chiefly to define remission and response in clinical trials of biologics and immunomodulators. It requires a 7-day patient diary of stools, pain, and wellbeing, so it is a retrospective 1-week assessment rather than a point-of-care score. It is not validated for isolated perianal or fistulizing disease (use the Perianal Disease Activity Index), for ostomy patients (stool counts are uninterpretable), or for pediatric Crohn's (use the PCDAI/wPCDAI).

Inputs used

  • Seven-day stool frequency
  • Seven-day abdominal pain
  • Seven-day general well-being
  • Complications
  • Antidiarrheal use
  • Abdominal mass
  • Hematocrit
  • Weight

Clinical interpretation

Scores of 150 or below indicate clinical remission (quiescent disease); above 150 indicates active disease. Trials commonly stratify as mild-to-moderate (roughly 150-220), moderate-to-severe (about 220-450), and severe/fulminant (above 450). A drop of 70 points (CDAI-70) is a conventional clinical response threshold and 100 points (CDAI-100) a more stringent one; remission is a score under 150. These bands drive trial eligibility and endpoint adjudication, but in practice the CDAI correlates poorly with mucosal inflammation, so a low score does not confirm endoscopic or biochemical healing.

Worked example

Consider a 60 kg woman: 28 liquid stools over 7 days (28x2 = 56); pain scores summing to 14 over the week (14x5 = 70); wellbeing scores summing to 12 (12x7 = 84); two complications, arthralgia and an anal fissure (2x20 = 40); taking loperamide (1x30 = 30); no abdominal mass (0); hematocrit 33% so (47 - 33)x6 = 84; body weight 12% below standard (12x1 = 12). Total = 56 + 70 + 84 + 40 + 30 + 0 + 84 + 12 = 376, indicating moderately-to-severely active disease.

Limitations and safety notes

The CDAI is heavily driven by subjective, symptom-based items (pain, wellbeing, stool frequency contribute the bulk of the weighting), so functional overlap such as irritable bowel symptoms, bile-salt diarrhea, or bacterial overgrowth can inflate the score without active inflammation, while it correlates weakly with CRP and endoscopic activity. The hematocrit and weight terms make it unreliable in anemia of other causes or obesity, and the 7-day diary burden introduces recall and adherence error. It is invalid in stoma patients, perianal-predominant disease, and children.

Frequently asked questions

What CDAI score defines remission?

A score of 150 or below defines clinical remission (quiescent disease). Scores above 150 indicate active disease, and scores above 450 indicate very severe disease.

What is the difference between CDAI-70 and CDAI-100 response?

Both are trial response criteria measuring a fall from baseline: CDAI-70 is a decrease of at least 70 points and CDAI-100 a decrease of at least 100 points. CDAI-100 is the more stringent and clinically meaningful threshold.

Why does my patient have a high CDAI but a normal CRP and clear colonoscopy?

The CDAI is dominated by subjective symptom items, so functional overlap (coexisting IBS, bile-acid diarrhea, or SIBO) can produce a high score without active inflammation. This symptom-inflammation discordance is a well-known limitation; objective markers should guide treatment decisions.

Can I use the CDAI for perianal or pediatric Crohn's disease?

No. The CDAI was derived in adults with luminal small-bowel and colonic disease. Use the Perianal Disease Activity Index for fistulizing perianal disease and the weighted PCDAI for children.

Why does the CDAI need a 7-day diary?

Three of the eight variables (stool frequency, abdominal pain, and general wellbeing) are summed over the preceding 7 days from a daily patient diary, so the score reflects a full week of symptoms rather than a single clinic snapshot.

References

  • Best WR, Becktel JM, Singleton JW, Kern F Jr. Development of a Crohn's disease activity index. National Cooperative Crohn's Disease Study. Gastroenterology. 1976. PMID: 1248701.
  • Lichtenstein GR, Loftus EV, Isaacs KL, Regueiro MD, Gerson LB, Sands BE. ACG Clinical Guideline: Management of Crohn's Disease in Adults. Am J Gastroenterol. 2018. PMID: 29610508.

Editorial review and citation methodology

Reviewed by the Quick Medical Calculator Editorial Team. Last reviewed: June 24, 2026. The review checks calculator inputs, intended population, interpretation, limitations, and source alignment.

  • Prefer original validation studies for scoring systems and prediction tools.
  • Use current specialty society guidance, transplant allocation policy, public health guidance, or regulator resources when they govern clinical use.
  • Include limitations and safety notes when a calculator is population-specific, context-dependent, or unsuitable as a standalone decision tool.

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