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Your doctor needs information from you to help diagnose ulcerative colitis (UC). Diagnosing UC starts when you and your doctor have a discussion about your health (called a medical history). It's important to share information about your medical history, including the symptoms you're experiencing, and any recent travel (to rule out bacterial, viral, or parasitic infections). Also, be sure to tell your doctor about all the medications, vitamins, or supplements you're taking and whether you have any drug allergies. This information can help your doctor determine whether there is a drug interaction with or a drug allergy to a UC medication. Your doctor will also want to know if there is a family history of digestive disorders, including inflammatory bowel disease (IBD). After a careful physical exam, blood tests, and a stool sample, your doctor may order other tests as well to determine if you have UC.

Common tests for diagnosis

In addition to the physical exam, you may be asked to get a blood test. Other tests, including a sigmoidoscopy or a colonoscopy, are commonly performed as well.


A colonoscopy is an exam that uses a tool called a colonoscope to view the entire colon (large intestine) and rectum. The colonoscope has a small camera attached to it that transmits a video image of the colon tissue. This exam usually lasts 30 to 60 minutes, and a doctor may take a biopsy.

To prepare for a colonoscopy, the colon must be emptied. This may involve maintaining a clear liquid diet for 24 hours or longer prior to the test, taking laxatives in pill or liquid form, and/or using an enema.


A sigmoidoscopy is a similar exam but views only the rectum and part of the colon on the left side of your body. The colon should also be clear for a sigmoidoscopy. You may be asked to maintain a clear liquid diet for 24 to 48 hours before the test. Enemas can be used to clear the colon, but should not be used in patients with a UC flare. This is because an enema may increase the blood flow within the inner lining of the colon, which can be mistaken as UC inflammation.

If your doctor orders either of these tests, it is very important that you follow the prep instructions carefully and completely, so the doctor is able to see the colon lining clearly.

These tests are used to help determine if you have UC and the extent and severity of your UC. They may also be used later on to find out whether or not your disease has become better or worse. Both tests may be done by a specialist in a doctor’s office, clinic, or hospital.