Strengths and limitations of the Crohn's disease activity index, revealed by an objective gut lavage test of gastrointestinal protein loss

Background: Several factors contribute to overall illness in patients with inflammatory bowel disease. The Crohn's disease activity index (CDAI), correlates closely with symptoms and is widely used to assess efficacy in clinical trials; previous work indicated that a gut lavage test for protein-losing enteropathy (PLE) may measure the same symptomatic, acute inflammatory component of overall inflammatory bowel disease illness. Methods: Results of the protein-losing enteropathy test have been compared with the CDAI in 42 routinely presenting inflammatory bowel disease patients, and in 26 patients with ileostomies, eight children and five psychologically disturbed individuals with inflammatory bowel disease. Results: For general adult patients with Crohn's disease or ulcerative colitis, concentrations of proteins in gut lavage fluid, particularly IgG, correlated well with CDAI. However, high CDAIs (> 150) were obtained in patients with fibrous small bowel strictures, in psychologically disturbed patients and also in five of seven patients in whom a provisional diagnosis of inflammatory bowel disease was subsequently shown to be wrong. In all these cases, normal values in the protein-losing enteropathy test reinforced the clinical judgement of a low probability of acute inflammatory activity of the inflammatory bowel disease. In the children, results of the protein-losing enteropathy test were positive in all cases; this was consistent with the clinical diagnosis, but CDAI values ranged from -66 to 275. In ileostomy patients, concentrations of IgG in gut lavage fluid discriminated well between groups judged, globally, to have either acute inflammatory activity or inactive disease, but there was no significant association with CDAI. Conclusions: These data confirm that, in most inflammatory bowel disease patients, the CDAI measures a true biological phenomenon which also causes gastrointestinal protein loss. However there are a number of situations where the CDAI is inappropriate or unreliable; for these, tests based on whole gut lavage, including the protein-losing enteropathy test, offer an alternative method to measure the efficacy of pharmacological and other anti-inflammatory therapies.