Diagnosing Ulcerative Colitis

Making an accurate diagnosis of ulcerative colitis often requires ruling out other possible causes (such as infection, Crohn’s disease, diverticulitis or colon cancer, among others) first before making a final determination. Since there is no single test that can make a definitive diagnosis of ulcerative colitis, your doctor will typically gather information from several sources to understand your symptoms. This information gathering may begin with a physical exam and a health history and be followed up with lab tests and scans. Here are some of the most common ways doctors go about making the diagnosis of ulcerative colitis.

Stool sample

One of the first lab tests your doctor may perform might be to collect a stool sample to check for the presence of white blood cells, which indicates an inflammatory disease. A stool that tests positive for inflammation is not enough to make a confirmed diagnosis of ulcerative colitis but it will prompt your doctor to investigate further with additional tests. A stool test can also rule out other similar disorders, such as those caused by parasites, viruses or bacteria.

Blood test

A blood test may be ordered to see if you have anemia (a condition where there are not enough red blood cells) and to look for signs of infection and inflammation of the intestine.

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This test enables your doctor to look inside your entire colon (large intestine) using a thin, flexible, lighted tube equipped with a tiny camera. A colonoscopy reveals any inflammation in the intestine. During this procedure, a small sample of tissue from the intestine might be taken (called a biopsy) and sent to the lab for analysis to help confirm the diagnosis.

Flexible sigmoidoscopy

In this procedure, the doctor also uses a flexible, lighted tube with a small camera but the sigmoidoscopy only looks at the first third of your colon (called the sigmoid colon) located on the left side. A sigmoidoscopy may be ordered if the inflammation of your colon is severe. The potential downside of a sigmoidoscopy is that it can’t view potential problems higher in the colon.


A standard X-ray may be performed on your abdominal area to rule out the existence of an enlarged and dilated colon (called toxic megacolon) or the possibility of a perforated colon.

Computerized tomography (CT)

You might also have a CT scan, which is a special type of X-ray that provides more detail than a standard X-ray. This test allows your doctor to see the entire colon and better understand the extent and location of the inflammation.

Magnetic resonance imaging (MRI)

Instead of a CT scan your doctor may order an MRI, which uses a magnetic field and radio waves to create highly defined images of the organs and tissues. The MRI can produce similar results as the CT scan. The advantage of MRI over the CT scan is that there is no radiation exposure.

Barium enema X-ray

In some instances, a barium enema X-ray may be recommended. During a barium enema X-ray a chalky liquid is injected into the colon through the rectum to outline the colon so it can be seen with an X-ray. In most cases, a colonoscopy or sigmoidoscopy will be preferred over the barium enema X-ray and serves as a more accurate means of viewing the colon. There is a very limited role for this test

Suggested: Symptoms of Ulcerative Colitis

Though most people will not have all of these tests performed in order to make a correct diagnosis, it may be necessary to have several of them to accurately confirm the diagnosis of ulcerative colitis.

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