Gastroenterology
Crohn’s Disease Activity Index (CDAI)
Enter symptom counts, complication list, hematocrit, and antidiarrheal use to compute the CDAI. The result guides treatment intensity and defines remission or flare severity.
Weighted contribution: 2 × value
Over the past 7 days
Weighted contribution: 5 × value
Weighted contribution: 7 × value
Weighted contribution: 20 × value
Arthritis/arthralgia, iritis/uveitis, erythema nodosum, pyoderma gangrenosum, aphthous ulcers, anal fissure/fistula/abscess, fever >37.8°C in 7 days
Weighted contribution: 10 × value
Weighted contribution: 6 × value
Weighted contribution: 1 × value
((Ideal weight – Actual weight) / Ideal weight) × 100. Use 0 if weight ≥ ideal.
Component summary
- Stools ×2: 8
- Pain ×5: 5
- Well-being ×7: 7
- Complications ×20: 20
- Antidiarrheal: 30
- Abdominal mass ×10: 0
- 6 × (47 – Hct): 42
- Weight factor: 5
Total CDAI
117
Remission threshold < 150
CDAI < 150 = clinical remission. Continue maintenance therapy and routine monitoring.
Align treatment with STRIDE-II targets; consider therapeutic drug monitoring and mucosal healing goals.
How to Use This Calculator
Gather 7-day symptom diary
Average stool frequency, abdominal pain, and well-being scores across the past week for accuracy.
Count complications carefully
Include extraintestinal manifestations and fever >37.8°C. Each counts as one complication.
Use sex-specific hematocrit adjustment
Original CDAI uses 47 for men and 42 for women. Adjust the formula if needed for female patients.
Formula
CDAI = (Number of liquid/soft stools ×2) + (Abdominal pain rating ×5) + (General well-being rating ×7) + (Complications count ×20) + 30 (if antidiarrheal use) + (Abdominal mass rating ×10) + 6 × (47 – Hct) + (% weight deviation ×1)
For women, replace 47 with 42 in the hematocrit term.
Remission: <150 • Mild: 150–219 • Moderate: 220–299 • Severe: 300–449 • Very severe: ≥450.
Full Description
The Crohn’s Disease Activity Index (Best et al., 1976) quantifies disease activity for clinical trials and practice. It emphasizes patient-reported symptoms, objective markers (hematocrit, weight), and complication burden. While widely used, CDAI may not fully capture transmural disease or subclinical inflammation.
Treatment decisions should incorporate endoscopic findings, CRP/fecal calprotectin, imaging, and therapeutic goals such as mucosal healing. CDAI has limited utility in perianal disease or stricturing phenotypes without luminal symptoms.
Frequently Asked Questions
How do I account for opioid use?
Opioids that reduce stool frequency may mask symptoms. Document opioid use and interpret CDAI cautiously.
Is CDAI valid in pediatric patients?
No. Use the Pediatric Crohn’s Disease Activity Index (PCDAI) or weighted PCDAI for children.
What if hematocrit is affected by anemia of chronic disease?
Hematocrit reflects systemic inflammation and bleeding. Interpret trends along with iron studies and transfusion history.
Does CDAI guide biologic selection?
It helps quantify activity but does not dictate agent choice. Combine with disease phenotype, prior treatment response, and biomarkers.