Crohn’s Colitis vs Ulcerative Colitis: How Doctors Tell Them Apart
Last Updated Jan 15, 2026
Crohn’s disease and ulcerative colitis are the two main types of inflammatory bowel disease (IBD), and they can overlap in symptoms like diarrhea, belly pain, and fatigue. When Crohn’s inflammation is limited to the colon (large intestine), it is often called Crohn’s colitis. This name can be confusing, because it does not mean both Crohn’s disease and ulcerative colitis are present. It describes where Crohn’s disease is showing up. Since ulcerative colitis also affects the colon, Crohn’s colitis vs ulcerative colitis can be hard to tell apart at first, especially early in the disease. [1]
Pattern and depth: what doctors see on scopes and scans
One of the biggest clues in Crohn’s vs UC (ulcerative colitis) is the pattern of inflammation. On colonoscopy, ulcerative colitis typically starts in the rectum and extends upward in a continuous inflammation pattern, with no normal gaps. Crohn’s disease often has skip lesions, meaning inflamed areas are separated by healthier-looking tissue, and it can affect any part of the digestive tract from mouth to anus. Another key difference is depth. Ulcerative colitis mainly affects the inner lining of the colon (the mucosa). Crohn’s disease can involve deeper layers of the bowel wall, which is why complications like narrowing (strictures) and tunnels (fistulas) are more associated with Crohn’s. When Crohn’s is limited to the colon (Crohn’s colitis), it may still show Crohn’s-style patterns, such as patchiness or deeper injury, even without small-bowel disease. [2]
Because no single finding is perfect, diagnosis often uses a combination of information, including symptoms, blood and stool tests, colonoscopy, and imaging. Imaging can be especially helpful when Crohn’s is suspected beyond the colon, since some tests can look at parts of the small intestine that are hard to reach with standard scopes. [3]
Biopsy differences (Crohn’s vs UC), indeterminate colitis, and why diagnoses can change
During colonoscopy, small tissue samples (biopsies) are taken and reviewed under a microscope. These biopsy differences (Crohn’s UC) can add important clues, but they do not always provide a simple answer. In general, ulcerative colitis tends to show inflammation limited to the surface layers, while Crohn’s may show deeper injury and may include granulomas (small clusters of immune cells) in some cases. Granulomas can strongly support Crohn’s, but they are not present in everyone, and biopsies only sample tiny spots, so results can be incomplete. [4]
Sometimes the colon inflammation does not clearly match classic Crohn’s or classic ulcerative colitis. In those situations, a healthcare team may use terms like indeterminate colitis or IBD-unclassified (inflammatory bowel disease unclassified). [5] This uncertainty is fairly common, and research reviews describe indeterminate colitis in roughly 5 to 15 percent of IBD cases, with many people later being reclassified as Crohn’s disease or ulcerative colitis as more information appears over time (from repeat biopsies, imaging, or the way the disease behaves). [6]