𧬠Crohn's Activity Index (CDAI)
The 8-component weighted score. Remission is under 150.
Standard weight: use ideal body weight. Our ideal weight calculator computes it. Complications: arthritis, eye inflammation, skin lesions, anal disease, other fistula, fever over 37.8 C.
For clinical education only. Crohn's management belongs to your gastroenterologist.
The Crohn's Disease Activity Index has measured Crohn's severity since Best and colleagues published it in 1976. Eight components, each weighted by how much it mattered in the original regression, sum to a score where under 150 means remission and over 450 means severe disease. Trials still use CDAI response (a 100-point drop) as their yardstick. This calculator scores all eight components with their proper weights.
How to Use This Calculator
Enter the 7-day averages for symptoms, check the complication count, and add the lab and weight numbers.
Enter average liquid or soft stools per day, pain grade, and wellbeing grade over the past 7 days.
Count extraintestinal complications: arthritis, eye inflammation, skin lesions, anal disease, other fistula, fever over 37.8 C.
Add antidiarrheal use, abdominal mass, hematocrit with sex baseline, and current vs standard weight.
Read the total: under 150 remission, 150-219 mild, 220-450 moderate-severe, over 450 severe.
The Eight Components and Weights
The weights reveal what the originators learned: subjective wellbeing (x7) and pain (x5) dominate because they track the patient's lived disease, while stool count (x2) is noisier. The hematocrit deviation, (47 - Hct) for men or (42 - Hct) for women times 6, smuggles in anemia from chronic inflammation or blood loss. Weight deviation, percent below standard weight, captures the nutritional toll. A 100-point drop defines clinical response in trials; remission is the under-150 line.
CDAI's famous criticism is that it correlates imperfectly with actual gut inflammation: symptoms can rage with a calm bowel (IBS overlap, strictures) or smolder silently with active ulcers. That is why modern practice pairs it with objective markers: fecal calprotectin, CRP, and endoscopy. The Harvey-Bradshaw Index is the simplified bedside cousin (5 unweighted items), but CDAI remains the trial standard, so knowing your number lets you read research about your own disease.
Worked Example
4 liquid stools/day (8), moderate pain (10), poor wellbeing (14), one complication such as arthritis (20), no antidiarrheal (0), no mass (0), hematocrit 38 in a man: (47-38) x 6 = 54, weight 65 vs standard 70: (1 - 65/70) x 100 = 7.1. Total = 113: remission range, though the symptom components show the patient does not feel in remission, which is exactly the CDAI-endoscopy disconnect worth discussing with the gastroenterologist. Change stools to 8/day and pain to severe: 16 + 15 + 14 + 20 + 54 + 7.1 = 126... still under 150. Now add definite mass (50) and two complications (40): 216, mildly active. The weights mean single symptoms rarely move the needle alone; it takes the full picture.
What the Bands Mean for Treatment
Remission under 150 is the target of maintenance therapy: keep doing what is working. Mildly active disease (150-219) often gets a therapy optimization or a short steroid bridge. Moderate-severe (220-450) is where biologics, dose escalation, or combination therapy enter. Above 450 signals severe disease needing urgent reassessment, sometimes hospitalization. These are patterns, not protocols: the gastroenterologist weighs CDAI against calprotectin, imaging, and history. If your CDAI says remission but you feel terrible, say so loudly; the score is a tool, and you are the patient.
Track the trend, not just the number. A CDAI falling from 320 to 210 is a response even though 210 is not remission, and trials formalize this as the 100-point response criterion. Keep a simple 7-day diary before appointments: stool count, pain, wellbeing. It takes two minutes a day and transforms the visit from guesswork to data. Bring the diary, not just the score.
CDAI vs Harvey-Bradshaw vs Objective Markers
Harvey-Bradshaw drops the weights and the labs: 5 items, one-day recall, quicker but cruder. Fecal calprotectin measures gut inflammation directly from a stool sample and often disagrees with CDAI in both directions. The modern treat-to-target approach (per the STRIDE guidelines) aims for clinical remission plus normalized biomarkers, not CDAI alone. Know all three numbers about yourself: the symptom score, the inflammation markers, and what the last scope showed. Together they describe the disease; alone, each one lies a little.
Related Calculators
Keep exploring: try our BMI calculator and fiber intake for the next piece of the picture.
For informational purposes only, not medical advice. Consult a healthcare professional.
Frequently Asked Questions
What is the CDAI score in Crohn's disease?
The Crohn's Disease Activity Index: 8 weighted components (stools, pain, wellbeing, complications, antidiarrheal use, abdominal mass, hematocrit deviation, weight deviation) summed to a score. Under 150 is remission, 150-219 mild, 220-450 moderate-severe, over 450 severe.
What CDAI score indicates remission?
Below 150. Clinical response in trials is defined as a drop of at least 100 points. Remission is the treatment target, though modern care also aims for normalized inflammatory markers.
How is CDAI calculated?
Each component is multiplied by its weight (x2 stools, x5 pain, x7 wellbeing, x20 per complication, x30 antidiarrheal, x10 mass, x6 hematocrit deviation, x1 weight deviation) and summed. This calculator applies all weights automatically.
What is the difference between CDAI and Harvey-Bradshaw?
Harvey-Bradshaw is the simplified bedside version: 5 unweighted items with one-day recall. CDAI uses 8 weighted components over 7 days plus labs. CDAI remains the clinical trial standard; Harvey-Bradshaw suits quick clinic checks.
Can CDAI be normal with active Crohn's?
Yes, and this is its well-known limitation. CDAI measures symptoms and indirect markers, which correlate imperfectly with actual gut inflammation. Objective markers like fecal calprotectin and endoscopy complement it.
What does a CDAI over 450 mean?
Severely active disease by the index definition. It usually prompts urgent gastroenterology reassessment and often treatment escalation or hospitalization. Do not wait for a routine appointment with a score this high.
How often should CDAI be assessed?
At each gastroenterology visit and when symptoms change, using a 7-day symptom diary for accuracy. In trials it is measured on schedule; in practice, before appointments and during flares.
Does the CDAI include lab work?
Indirectly: the hematocrit deviation component ((47-Hct) for men, (42-Hct) for women, x6) captures anemia from inflammation or blood loss. CRP and calprotectin are not part of CDAI but are tracked alongside it.
What is considered a response to treatment by CDAI?
A decrease of at least 100 points from baseline. Remission (<150) is the stronger target. Both definitions come from clinical trial conventions and are used to judge whether a therapy is working.
Who developed the CDAI?
Best, Becktel, Singleton, and Kern published it in 1976 from the National Cooperative Crohn's Disease Study data, using regression to weight the components. It has been the standard Crohn's activity measure for nearly 50 years.