Diagnosing Ulcerative Colitis: What Doctors Look For

Find out how inflammation in the colon shows up in tests.

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Some of the textbook symptoms of ulcerative colitis (UC)—like frequent diarrhea or abdominal pain—are signs of a number of digestive disorders. Plus, UC can present almost identically to Crohn’s disease, another type of inflammatory bowel disease. So how do doctors know if it’s UC or Crohn’s—or something else entirely?

The key to diagnosing UC is looking for signs of inflammation, and noting where the inflammation is occuring. To do this, doctors use a combination of your medical history, physical exam, blood tests, endoscopies, and other imaging tests.

Medical History

Your medical history may help doctors diagnose ulcerative colitis because it can reveal common risk factors of UC, such as smoking or having a relative with inflammatory bowel disease. Although it’s unclear how (or if) UC is passed genetically, having a family member with UC does seem to increase the risk of developing it.

Your medical history might also reveal comorbidities that are often linked to inflammatory bowel diseases like UC. If someone has inflammation in the colon, they are more likely to have systemic inflammation elsewhere in the body. Therefore, the presence of another inflammatory condition—such as cardiovascular disease or celiac disease—could increase your risk of UC.

Stool Samples

Before more elaborate tests, doctors will likely request a stool sample. This analysis can help rule out other causes of diarrhea, such as a stomach virus, food poisoning, or parasite. A stool sample may also reveal blood in the stool, a common symptom of UC.


“The most common way to diagnose ulcerative colitis is to perform colonoscopy with biopsies,” says Sergey Khaitov, MD, a surgeon at Mount Sinai Hospital.

A colonoscopy is the use of a small camera attached to a lighted tube to examine the inside of the colon, inserted through the rectum. To get a biopsy, doctors will take a small sample of inflamed tissue from the colon. This can help doctors analyze the inflammation and what’s causing it.

Colonoscopies have an added benefit of detecting polyps or other precancerous changes, which is of special concern for people with UC. “One of the things that we emphasize about is that people with ulcerative colitis are at an increased risk of developing colon cancer,” says Todd B. Linden, MD, gastroenterologist. “It’s one of the most important reasons we want people to stay on their maintenance medications.”

Blood Tests

A routine blood test won’t diagnose you with UC, but it could detect anemia, which is a common problem among people with untreated UC. Anemia may occur due to bleeding in the colon or rectum, causing excess blood loss. Anemia can be caused by a number of conditions or from malnutrition, so more tests would be necessary before diagnosing with UC.

Another blood test doctors might use to diagnose UC is an antibody blood test. Antibodies are proteins made by the immune system when the body is trying to fight a disease, so a higher level of antibodies in the blood suggests an illness—potentially UC.

Imaging Tests

Doctors can utilize a variety of imaging tests to diagnose UC or get a better idea of how UC is affecting a specific patient, since the disease can vary in severity. Here are some of the imaging tests used by doctors, according to the Crohn’s and Colitis Foundation:

  • X-rays can show if intestines have narrowed, which may indicate inflammation. X-rays can also help rule out the possibility of bowel obstructions.
  • CT scans (or CAT scans) show a cross-sectional image of the bowel and can help detect any UC complications or rule out other conditions, such as appendicitis.
  • MRI can sometimes “show thickening or abnormal inflammation … in the large intestines, and sometimes it will help us to differentiate between Crohn’s disease and ulcerative colitis,” says Dr. Khaitov.
  • White blood cell scans can detect where white blood cells are clustering in your body, a sign of inflammation.
  • Endoscopic ultrasounds use an ultrasound probe to examine the lining of the intestines.

Although doctors have no cure for UC, about half of patients are able to live in remission (a period with no symptoms) in any given year thanks to current treatments for UC.