Objective: Crohn's disease is a highly distressful chronic disorder, characterized by frequent relapses. A symptom-based disease activity index was developed for use in epidemiological research.
Study design and setting: One hundred and six consecutive patients presenting to a tertiary referral hospital in Southern Germany in 2004-2005 participated in a questionnaire-based survey. As a reference standard, disease activity was assessed using a clinical index (Crohn's Disease Activity Index [CDAI], based on symptoms reported to physician, laboratory markers, and physician assessed signs). A linear regression equation was calculated based on the survey data on severity of symptoms (dependent variable: CDAI). Survey index scores (S-CDAI) were then calculated using the estimated coefficients for pain, stools, and general well-being in an independent data set.
Results: S-CDAI and CDAI showed moderate agreement (kappa=0.57 for relapse vs. remission). High activity (high S-CDAI) correlated negatively with high quality of life (disease specific: Short Inflammatory Bowel Disease Quality-of-Life Questionnaire; r=-0.67; generic: Short Form 36 physical summary score, r=-0.47). Test-retest reliability and sensitivity for change were good (intraclass correlation coefficient 0.81).
Conclusion: A useful, valid, and reliable disease activity score was developed, which will facilitate meaningful survey research in this chronic disorder.