Background: The Crohn's disease activity index (CDAI) is the most widely used Crohn's disease activity instrument, yet little is known about the methodological variation in its use.
Methods: A MEDLINE search was performed to identify authors of articles published from 1976 to 1997 in which the CDAI was used. A multiple-choice questionnaire was sent to all of the authors identified. Questions covered investigators' practice and research characteristics, and details of definitions and techniques applied in scoring the CDAI.
Results: A total of 208 authors were identified, and 100 valid responses were obtained. The respondents were experienced investigators, with 63% of the authors having used the CDAI for > or =7 years. Of these authors, 70% characterized themselves as working in an academic clinical practice, and 72% had participated in industry-sponsored drug studies in which the CDAI was used as an end point. Considerable variation was noted in the administration and scoring of the CDAI, including disagreement on the definition of "liquid or very soft stools," the recording of the number of stools, the recording of pain ratings, and the scoring of extraintestinal manifestations and fistulas. The recording of fever, the scoring for the use of opiates, and the standard for the weight variable also varied widely among respondents.
Conclusion: Considerable variation exists in the administration and implementation of the CDAI score among the pool of experienced researchers who were surveyed. This variation may affect the comparability of studies and may introduce random error into the measurement of the CDAI.