CDAI Calculator (Crohn's Disease Activity Index)
Calculate your Crohn's Disease Activity Index (CDAI) score with all 8 clinical variables. Classify disease severity: remission, mild, moderate, or severe.
About
The Crohn's Disease Activity Index (CDAI) quantifies disease severity in Crohn's disease patients using 8 clinical variables weighted by empirically derived coefficients. Developed by Best, Becktel, Singleton, and Kern in 1976, it remains the primary endpoint in clinical trials for IBD therapeutics. A score below 150 indicates clinical remission. Scores between 150 and 450 stratify mild-to-moderate disease. Scores above 450 indicate severe, potentially life-threatening flares requiring aggressive intervention. Miscalculation risks inappropriate therapy escalation or dangerous under-treatment. This tool implements the original Best et al. formula with all 8 factors and standard hematocrit references stratified by sex.
The CDAI approximates disease activity under the assumption that symptoms are recorded over a 7-day observation period. Factors 1 through 3 (liquid stools, abdominal pain, general well-being) require weekly summation. The hematocrit component uses sex-specific reference values: 47% for males, 42% for females. Body weight deviation is expressed as a percentage below a standard or ideal weight. Pro tip: record symptoms daily for 7 consecutive days before calculating. Single-day estimates introduce significant error.
Formulas
The CDAI is computed as the weighted sum of 8 clinical variables:
Where:
x1 = number of liquid/soft stools (7-day total)
x2 = abdominal pain rating sum (7-day, each day 0-3)
x3 = general well-being sum (7-day, each day 0-4)
x4 = number of extraintestinal complications (0-6)
x5 = antidiarrheal drug use (0 or 1)
x6 = abdominal mass (0, 2, or 5)
x7 = hematocrit deviation, computed as:
where Href = 47 for males, 42 for females.
x8 = percentage body weight below standard, clamped: max(0, 100 × (1 − WactualWstandard))
Reference Data
| Variable | Description | Multiplier | Input Type |
|---|---|---|---|
| Liquid/Soft Stools | Total number of liquid or very soft stools over 7 days | 2 | 7-day sum |
| Abdominal Pain | Sum of daily pain ratings (0 = none, 1 = mild, 2 = moderate, 3 = severe) over 7 days | 5 | 7-day sum (0-21) |
| General Well-Being | Sum of daily well-being ratings (0 = well, 1 = slightly below, 2 = poor, 3 = very poor, 4 = terrible) over 7 days | 7 | 7-day sum (0-28) |
| Complications | Number of listed complications currently present (arthritis/arthralgia, iritis/uveitis, erythema nodosum/pyoderma/aphthous stomatitis, anal fissure/fistula/abscess, other fistula, fever >37.8°C) | 20 | Count (0-6) |
| Antidiarrheal Use | Use of loperamide or opiates for diarrhea | 30 | 0 = No, 1 = Yes |
| Abdominal Mass | Presence of abdominal mass on examination | 10 | 0 = None, 2 = Questionable, 5 = Definite |
| Hematocrit Deviation | Absolute difference: expected hematocrit minus observed. Males: 47%; Females: 42%. Only positive deviations count. | 6 | Observed % |
| Body Weight | Percentage below standard (ideal) body weight. Negative values (overweight) clamped to 0. | 1 | % below standard |
| Score Interpretation Thresholds | |||
| Remission | CDAI < 150 | No active disease | |
| Mild | CDAI 150 - 219 | Mildly active Crohn's | |
| Moderate | CDAI 220 - 450 | Moderately active Crohn's | |
| Severe | CDAI > 450 | Severely active Crohn's | |
| Complication Checklist Items (Variable 4) | |||
| 1 | Arthritis or arthralgia | ||
| 2 | Iritis or uveitis | ||
| 3 | Erythema nodosum, pyoderma gangrenosum, or aphthous stomatitis | ||
| 4 | Anal fissure, fistula, or abscess | ||
| 5 | Other fistula (e.g., enterovesical) | ||
| 6 | Fever > 37.8°C (100°F) during the past week | ||