Objective
The Crohn's Disease Endoscopic Index of Severity (CDEIS) and Simple Endoscopic Score for Crohn's Disease (SES-CD) are commonly used to assess Crohn's disease (CD) activity; however, neither instrument has been fully validated. We assessed intra-rater and inter-rater reliability of these indices.

Design
Video recordings of colonoscopies obtained from 50 patients with CD who participated in an induction trial of a biological therapy were triplicated and reviewed in random order by four central readers. Data were used to assess intra-rater and inter-rater reliability for CDEIS, SES-CD and a global evaluation of lesion severity (GELS). Subsequently, readers participated in a consensus process that identified common sources of disagreement.

Results
Intraclass correlation coefficients (ICCs) for intra-rater reliability for CDEIS, SES-CD and GELS (95% CIs) were 0.89 (0.86 to 0.93), 0.91 (0.89 to 0.95) and 0.81 (0.77 to 0.89), respectively, with standard error of measurement (SEM) of 2.10, 2.42 and 1.15. The corresponding ICCs for inter-rater reliability were 0.71 (0.63 to 0.76), 0.83 (0.75 to 0.88) and 0.62 (0.52 to 0.70), with SEM of 3.42, 3.07 and 1.63, respectively. Correlation between CDEIS and GELS was 0.75, between SES-CD and GELS was 0.74 and between CDEIS and SES-CD was 0.92. The most common sources of disagreement were interpretation of superficial ulceration, definition of disease site at the ileocolonic anastomosis, assessment of anorectal lesions and grading severity of stenosis.

Conclusions
Central reading of CDEIS and SES-CD had ‘substantial’ to ‘almost perfect’ intra-rater and inter-rater reliability; however, the responsiveness of these instruments is yet to be determined.