CDAI Calculator — Crohn's Disease Activity Index

The Crohn's Disease Activity Index (CDAI) is a numerical score developed by Best and colleagues in 1976 for the National Cooperative Crohn's Disease Study. It estimates Crohn's disease activity from 8 weighted clinical variables and produces a score from 0 to 600.

Each of the 8 components is multiplied by its weighting factor and the results are added: liquid stools × 2, abdominal pain × 5, general well-being × 7, extraintestinal complications × 20, antidiarrheal use × 30, abdominal mass × 10, hematocrit deviation × 6, and weight deviation × 1.

1) Number of liquid or very soft stools over 7 days. 2) Abdominal pain score (0–3 daily) summed over 7 days. 3) General well-being (0–4 daily) summed over 7 days. 4) Extraintestinal complications, one point each (0–6). 5) Antidiarrheal use (yes = 1, no = 0). 6) Abdominal mass (absent = 0, doubtful = 2, definite = 5). 7) Hematocrit deviation: 47 − Hct for men, 42 − Hct for women. 8) Weight deviation: 100 × (1 − current weight / standard weight).

Abdominal pain is rated daily as 0 = none, 1 = mild, 2 = moderate, 3 = intense, and the 7 daily ratings are summed (maximum 21). General well-being is rated daily as 0 = good, 1 = average, 2 = mediocre, 3 = poor, 4 = very poor, and summed over 7 days (maximum 28).

Six items, one point each if present during the week: arthritis or arthralgia, skin or mouth lesions, iritis or uveitis, perianal disease, other fistula, and fever above 37.8°C. The count (0–6) is multiplied by 20.

Hematocrit deviation is (47 − Hct) for men or (42 − Hct) for women, times 6 — it can be negative when hematocrit is above the reference. Weight deviation is 100 × (1 − current weight / standard weight) times 1, which is negative when current weight exceeds standard weight.

Scores below 150 are associated with quiescent disease (remission). Scores of 150–219 indicate mildly active disease, 220–450 moderately to severely active disease, and scores above 450 severely active disease.

In clinical studies, a decrease of more than 70 to 100 points from baseline is commonly used to define a clinical response, while complete remission is defined as a score below 150.

Much of the score comes from subjective items (well-being, pain intensity), different observers can calculate different scores for the same patient, and it requires a prospectively completed 7-day diary. The CDAI describes symptom activity — it is not a diagnosis and does not prescribe treatment; treatment decisions belong to a gastroenterologist.