detected through such assays remain to be robustly established, with initial results suggesting C. diff to be the predominant infectious determinant of adverse outcomes in patients with IBD (23). The diagnosis of UC requires a lower gastrointestinal endoscopic examination with histologic confirmation. For most patients, a complete colonoscopy including examination of the terminal ileum should be performed. This allows for assessment of the full extent of disease at diagnosis and can rule out distal ileal involvement, which can be seen with CD. Subsequent examinations can then assess response to therapy. However, in individuals with severe disease, a complete colonoscopy may be associated with a greater risk of perforation, and in this case, a sigmoidoscopy with biopsies is sufficient. Endoscopically, UC most often presents as a continuously inflamed segment involving the distal rectum and extending proximally. Endoscopic features of inflammation include loss of vascular markings, granularity and friability of the mucosa, erosions, and, in the setting of severe inflammation, deep ulcerations and spontaneous bleeding. The index colonoscopy should note involvement of the rectum and complete extent of inflammation. Proximal histologic extension may be seen even in endoscopically normal-appearing colon and may have implications for defining the extent of disease and subsequent surveillance intervals. Therefore, biopsies should be obtained from the proximal endoscopically normal-appearing colon even if the inflamed segment appears to be restricted to the distal colon. Similarly, even if the distal rectum appears endoscopically normal, separate biopsies from the rectum should be obtained because patchy histologic inflammation may be seen in 5%–30% of children with UC despite the absence of endoscopically visible inflammation (24). Routine upper endoscopic evaluation is not required in adults with a new diagnosis of UC and should be restricted to those with symptoms of upper gastrointestinal disease. While in the pediatric population, up to 8% of children with UC may have their diagnosis modified to CD based on upper endoscopic findings (25), such occurrences are less frequent in adult-onset disease (26). Gastritis and erosions may be seen in up to one-third of patients with UC (27). Imaging the small bowel with computed tomography (CT) or magnetic resonance imaging is also not routinely required in all patients with normal appearance of the terminal ileum on colonoscopy. However, in those with abdominal symptoms not explained by endoscopically active disease, with suspicion of CD (such as predominantly watery diarrhea, weight loss, or abdominal pain), or where proximal extent of involvement cannot be evaluated because of severity of inflammation, CT, magnetic resonance imaging, or video capsule endoscopy may be useful. Once a diagnosis of UC is made, determining the severity of disease becomes important. We have proposed new definitions of mildly, moderately, and severely active disease that incorporate both PROs and laboratory- and endoscopy-based values Active UC is frequently marked by an elevation in C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) (28,29). Although such markers are nonspecific and may be elevated with other causes of systemic inflammation, they often correlate with the endoscopic severity of disease (30). Such markers also have prognostic significance and have a role in predicting the