Abstract: The invention provides a method of diagnosing or predicting susceptibility to a clinical subtype of Crohn's disease in a subject having Crohn's disease by determining the presence or absence of IgA anti-I2 antibodies in the subject, where the presence of the IgA anti-I2 antibodies indicates that the subject has a clinical subtype of Crohn's disease. In one embodiment, a method of the invention is practiced by further determining the presence or absence in the subject of a NOD2 variant, anti-Saccharomyces cerevisiae antibodies (ASCA), IgA anti-OmpC antibodies, or perinuclear anti-neutrophil cytoplasmic antibodies (pANCA). The methods of the invention can be used to diagnose or predict susceptibility to a clinical subtype of Crohn's disease, for example, a fibrostenotic subtype, a subtype characterized by the need for small bowel surgery, or a subtype characterized by the absence of features of ulcerative colitis.

Abstract: Provided is a method of determining a risk of pouchitis development following a surgical procedure whereby colon is removed and an internal pouch is created in a patient with UC by determining a first pANCA titer, where the first pANCA titer is determined following the surgical procedure; determining a second pANCA titer at a later time; and comparing the first pANCA titer and the second pANCA titer, where a significantly elevated second pANCA titer indicates an increased risk of pouchitis development.