BACKGROUND: Several serologic tests, including anti-outer membrane porin C antibody (Omp C), are used for screening and as marker of disease course in inflammatory bowel diseases (IBD). Our aim was to investigate possible differences in Omp C level in patients with active and inactive IBD compared to controls.

METHODS: All blood samples were tested for Omp C. Disease activity was evaluated by Harvey Bradshaw Index, Simple Clinical Activity Index and Modified Pouchitis Disease Activity Index.

RESULTS: Blood samples were collected from 113 patients and 60 controls. Patients with active IBD did not have a higher level of Omp C than patients in remission. Surprisingly, in patients with active Crohn's disease a significantly lower level of Omp C was found compared with patients with inactive Crohn's disease (p < 0.05). All other groups among patients with IBD did have a significantly higher level of Omp C, compared with controls, including patients with acute gastroenteritis (p < 0.05). Although IBD patients with phylogroup B2 E. coli cultured from their fecal samples, were more likely to have a positive Omp C test (p < 0.05), this could not explain the low Omp C level in the subgroup of patients with active Crohn's disease.

CONCLUSIONS: Omp C titer was not raised in patients with active IBD compared with patients in remission. In addition, there was no difference in Omp C level in patients with active Crohn's disease compared with controls. These observations do not support the use of Omp C serology testing, either in disease activity assessment, or in screening for active Crohn's disease.