A diagnosis of ulcerative colitis (UC) is confirmed only after other possible causes of symptoms are ruled out, including:

  • Crohn’s disease
  • Infection
  • Irritable bowel syndrome (IBS)
  • Ischemic colitis (caused by a lack of oxygen to the large intestine)
  • Diverticulitis (inflammation on the inner walls of the intestinal tract)
  • Colon cancer

Along with your medical and family history and the results of your physical examination, your doctor can use a variety of tests to arrive at the correct diagnosis, including.


  • The most accurate test for detecting UC and determining its severity
  • Mainly used for evaluating colon-wall thickness. The thicker the wall from scarring due to inflammation, the more severe the disease.
  • How it’s done: The patient lies on a table that passes through a tube while powerful magnets are used to produce a series of internal images for analysis.
  • Done to view the rectum and colon and look for inflammation, ulcers, bleeding, narrowing, growths and colon cancer
  • Helps to rule out a diagnosis of Crohn’s disease or diverticulitis
  • How it’s done: A long, flexible, lighted tube is used to insert a tiny camera into the rectum to view the entire colon and transmit the real-time video image to a computer for analysis. Any polyps or other abnormal tissue can be painlessly biopsied during this procedure.

Flexible Sigmoidoscop

  • To examine the rectum and sigmoid (lower colon, just above the rectum) for signs of UC, particularly inflammation, ulcers, polyps and other abnormal growths
  • May be done instead of colonoscopy when the colon is severely inflamed
  • How it’s done: A flexible, lighted tube with a tiny camera on the end is used for video imaging of the sigmoid colon
  • Any polyps or other abnormal tissue can be painlessly biopsied during this procedure.

Computerized Tomography (CT Scan)

  • Mainly used for diagnosing UC complications and ruling out similar conditions
  • Can also reveal the extent of colon inflammation
  • How it’s done: Using x-ray contrast dye, cross-sectional scans are taken simultaneously from different angles and combined to construct a realistic image of the area under examination.

Magnetic Resonance Imaging (MRI)

  • To view and assess the entire large intestine using x-ray imaging

Barium Enema

  • Because of the risk of complications involving the colon, barium enema is usually done only to assess mild UC.
  • How it’s done: Using a tube inserted into the rectum, a barium solution and sometimes air are placed into the colon for x-ray imaging.

Stool Sample

  • To detect signs of inflammatory bowel disease, including white blood cells and blood
  • Also used to check for bowel infection and help rule out other disorders due to bacteria, viruses and parasites
  • How it’s done: The patient collects a stool sample for laboratory analysis.

Blood Tests

  • To check for anemia from colon or rectal bleeding, white blood cells signaling inflammation somewhere in the body, infection and antibodies that can help diagnose UC vs. Crohn’s disease
  • How it’s done: Blood is drawn from an arm vein or a finger for laboratory analysis

Standard X-ray

  • With severe UC symptoms, this test may be used to rule out an intestinal perforation and serious complication called toxic megacolon.
  • Also used to help rule out Crohn’s disease