Skip to Main Content
Diagnosis Gastroenterology

Ulcerative Colitis

Your doctor will ask about your medical history and perform a physical examination. Stool tests will then be performed to determine what is causing your diarrhea — colitis or something else. You will then undergo either a sigmoidoscopy or colonoscopy to exam your colon.


For a sigmoidoscopy, the doctor uses a special instrument called a colonoscope, which is a long, flexible tube that is about as thick as your index finger and has a tiny video camera and light on the end, to exam your rectum and lower part of your colon. During the procedure, everything will be done to help you be as comfortable as possible. Your blood pressure, pulse and the oxygen level in your blood will be carefully monitored.

Your doctor will do a rectal exam with a gloved, lubricated finger; then the lubricated colonoscope will be gently inserted. As the scope is slowly and carefully passed, you may feel as if you need to move your bowels, and because air is introduced to help advance the scope, you may feel some cramping or fullness. Generally, however, there is little or no discomfort. Occasionally, some abdominal pressure, which may be provided by your nurse, or a change in position may be needed to avoid looping of the colonoscope within the abdomen. Your doctor will advance the scope until he or she has examined the left side of the colon. Afterwards, the scope is then carefully withdrawn while a thorough exam of the colon is performed. At this point in the exam, your doctor will use the colonoscope to look closely for any polyps or other problems that may require evaluation, diagnosis or treatment. The procedure typically takes between 10 and 15 minutes.


The term "colonoscopy" means looking inside the colon. The colon, or large bowel, is the last portion of your digestive tract. Its main function is to store unabsorbed food products prior to their elimination. Colonoscopies are performed by a gastroenterologist, a doctor specially trained in digestive disorders. Your doctor will be assisted by specially trained nurses and technicians.

The procedure is performed using a colonscope. This device is a long, flexible tube that is about as thick as your index finger and has a tiny video camera and light on the end. By adjusting the various controls on the colonscope, the gastroenterologist can carefully examine the inside lining of the colon from the anus to the cecum. The colonoscope contains a channel that allows instruments to be passed in order to take tissue or stool samples, remove polyps and provide other therapy.

The high quality picture from the colonoscope is shown on a television monitor. Colonoscopy provides the best imaging of the colon at present. It is a more precise examination than X-ray studies. This procedure also allows other instruments to be passed through the colonoscope. These may be used, for example, to painlessly remove a suspicious-looking growth or to take a biopsy, during which a small piece of tissue is obtained, for further analysis. In this way, colonoscopy help doctors assess whether surgery is necessary as well as what type of surgery may be needed.

UCSF Health medical specialists have reviewed this information. It is for educational purposes only and is not intended to replace the advice of your doctor or other health care provider. We encourage you to discuss any questions or concerns you may have with your provider.