Characteristics of inflammatory bowel disease serology in patients with indeterminate colitis

Goals and Background: Inflammatory bowel disease (IBD) serology testing is often used in patients with indeterminate colitis (IC) to help distinguish between ulcerative colitis (UC) and Crohn’s disease (CD). We investigated the performance of serology testing in predicting future diagnosis in this setting. Study: This was an observational study of individuals with IC at a single center who underwent IBD serology testing [anti-Saccharomyces cerevisiae antibody (ASCA), perinuclear anti-neutrophil cytoplasmic antibody (pANCA), and anti-outer membrane porin C antibody (anti-OmpC)] and had at least 12 months follow-up from the time of serology test results. Results: A total of 117 individuals with IC and with 1-year follow-up data were enrolled. All IC patients had endoscopic and histologic evidence of colitis at enrollment. One year after serology testing, 58 (50%) individuals with IC were diagnosed with UC, 49 (42%) with CD, and 10 (9%) remained labeled with IC. The sensitivity/specificity of an initial positive pANCA for a subsequent diagnosis of UC was 78%/44%. For ASCA and anti-OmpC, the results were 18%/84% and 27%/75%, respectively, for a subsequent diagnosis of CD. A positive pANCA test was associated with a likelihood ratio (LR) of 1.4 [95% confidence interval (CI), 1.1-1.8] for a subsequent diagnosis of UC at 1 year. Neither positive ASCA (LR 1.1; 95% CI, 0.5-2.5) nor anti-OmpC (LR 1.1; 95% CI, 0.6-2.0) was associated with a subsequent diagnosis of CD in patients with IC. Conclusions: The disease phenotype in the majority of individuals initially labeled with IC evolved to be more consistent with either UC or CD on follow-up. pANCA, ASCA, and anti-OmpC, individually, were of limited utility in predicting a patient’s subsequent disease phenotype.