The discrepancy in response rates between the ASTIC study (44%) and the Northwestern study (73%) are likely due to several factors. First, the Northwestern population included patients with less severe Crohn's disease than the ASTIC trial. The Northwestern patients were eligible provided that the patient failed anti-TNF therapy while the ASTIC trial used stricter eligibility criteria. In addition, the ASTIC trial required endoscopic evidence of active Crohn's disease and therefore excluded patients whose disease activity scores reflected causes other than active inflammatory Crohn's disease, while the Northwestern trial did not. The CDAI score can be inflated from symptoms related to functional bowel disease and not the active inflammatory disease which is the target of immunosuppressive therapies. Active inflammatory mucosal disease is the greatest predictor of disease free survival and improves the reliability of the CDAI as a disease activity index. Finally, in an unknown number of patients the primary endpoint for the Northwestern patients was assessed on the basis of telephone report from patients that were asymptomatic and not on immunosuppressants, rather than the more rigorous CDAI score.