Ulcerative Colitis vs IBS: How to Tell the Difference + Which Tests Matter
Last Updated Jan 15, 2026
Stomach pain, urgency, diarrhea, and bloating can show up in both ulcerative colitis (UC) and irritable bowel syndrome (IBS). That overlap is why searches for “ulcerative colitis vs IBS” are so common, and why it can feel confusing at first. A helpful way to start is to remember that UC is a type of inflammatory bowel disease (IBD), meaning it involves inflammation and tissue injury, while IBS is a symptom-based condition without visible damage. Getting the right label matters because the next steps, including which tests are most useful, are different.
UC symptoms vs IBS: what overlap looks like, and what points to inflammation
UC affects the colon (large intestine) and rectum, causing inflammation and sores (ulcers) in the inner lining. Classic clues include diarrhea that may contain blood or mucus, strong urgency, and cramping that often happens with bowel movements. This is why “blood in stool UC” is treated as an important symptom to share with a clinician, even if it comes and goes. [1]
IBS can also bring abdominal pain, bloating, and changes in bowel habits (diarrhea, constipation, or both). The difference is that IBS is not defined by inflammation or damage that can be seen on routine testing of the digestive tract. It is considered a disorder of gut-brain interaction (how the brain and gut communicate). [2]
Because IBD vs IBS can look similar day to day, clinicians often focus on “alarm” features that raise concern for something beyond IBS, such as rectal bleeding, unintentional weight loss, nighttime diarrhea, or iron-deficiency anemia. These signs do not confirm UC, but they do support getting evaluated promptly, often by a gastroenterologist (a “GI”), especially when symptoms persist or worsen. [3]
Which tests matter: fecal calprotectin, blood work, stool studies, and colonoscopy
When symptoms overlap, testing usually focuses on two goals: (1) checking for inflammation and (2) ruling out other causes, such as infection. For UC, common starting points include blood tests (for anemia and other signs of illness), stool tests (including tests that can look for intestinal inflammation and infections), and then endoscopy of the large intestine (colonoscopy or flexible sigmoidoscopy) with biopsies. A biopsy is a small tissue sample examined under a microscope, and it is a key part of confirming UC and checking what type and pattern of inflammation is present. [4]
One test that often comes up in “fecal calprotectin IBS vs IBD” discussions is fecal calprotectin, a stool marker linked to inflammation in the intestines. In general, higher levels make inflammatory conditions like UC more likely, while lower levels make a non-inflammatory condition like IBS more likely (though no single test is perfect). NICE (the UK National Institute for Health and Care Excellence) recommends fecal calprotectin testing as a tool to help distinguish IBD from non-inflammatory conditions like IBS and guide appropriate referral. [5]
Questions to consider bringing to a visit (primary care or when to see a GI) include:
- “Which findings suggest inflammation rather than IBS symptoms?”
- “Would fecal calprotectin or other stool testing help decide next steps?”
- “If a colonoscopy is recommended, will biopsies be taken even if the lining looks normal?”
- “Could an infection, medication effect, or another condition be part of the picture?”