CDAI calculator (Crohn's Disease Activity Index)

The CDAI formula multiplies various clinical variables by specific weighted regression coefficients derived from historical validation studies. The core mathematical expression sums these weighted components: CDAI = (2 × Stool) + (35 × Pain) + (49 × Wellbeing) + (20 × Complaints) + (30 × Drugs) + (10 × Mass) + (6 × Hematocrit) + Weight Difference. Here, 'Stool' represents liquid or soft stool frequency over seven days, 'Pain' and 'Wellbeing' are rated daily sums, 'Complaints' accounts for associated extra-intestinal symptoms like arthritis or fever, 'Drugs' reflects antidiarrheal and immunomodulatory medication use, 'Mass' indicates an abdominal mass presence, 'Hematocrit' adjusts for anemia based on biological sex, and 'Weight' measures percentage deviation from standard body weight.

Consider a patient evaluated over a seven-day period with the following recorded clinical inputs: Liquid stool sum of 15, abdominal pain score of 8, general wellbeing score of 10, and two associated complaints (such as arthritis and low-grade fever). The patient takes antidiarrheal medication (value 1), presents with no palpable abdominal mass (value 0), has a male hematocrit of 41% (which yields a standard deviation factor), and has a 5% below-ideal weight differential. Plugging these into the equation: Stool component = 2 × 15 = 30; Pain component = 35 × 8 = 280; Wellbeing component = 49 × 10 = 490; Complaints component = 20 × 2 = 40; Drugs component = 30 × 1 = 30; Mass component = 10 × 0 = 0; Hematocrit component = 6 × (45 - 41) = 24; and Weight component = 5 (representing 5% deviation). Summing these values together yields a total CDAI score of 499, indicating severe active disease activity.

Accurate CDAI scoring heavily depends on meticulous seven-day prospective data logging rather than retrospective guesswork. Patients should maintain a daily symptom diary for stool consistency, pain levels, and general state to prevent recall bias. Additionally, always verify that lab values like hematocrit match the correct sex-specific baseline formulas to ensure precision in the final composite score.