The first step in diagnosing ulcerative colitis (UC) is a visit to a physician for a medical history and physical examination. Patients may be asked about the extent and duration of their symptoms, any family history of inflammatory bowel disease (IBD), as well as their eating, drinking or smoking habits.   

Blood tests and stool samples may also be required. Blood tests can identify low red blood cell counts (anemia) and high white blood cell counts (which may indicate inflammation or infection). A stool sample analysis (fecal test) can identify bleeding or infection of the large intestine.  

Various diagnostic tests may be used to determine if a patient has UC. They may also be used to rule out evidence of infections or other diseases (such as Crohn’s disease, irritable bowel syndrome [IBS], colorectal cancer or diverticulitis) that may be causing the symptoms. These tests include:

• Colonoscopy. Examination of the entire large intestine using a small, flexible tube (with a light and camera) inserted through the anus. This procedure allows physicians to identify the severity and extent of disease. Patients take a laxative prior to the procedure to cleanse the large intestine and are sedated during the procedure.
  
  During colonoscopy, a  tissue sample (biopsy) may be taken for evaluation under a microscope. This may help identify the type of IBD that is present. For example, if granulomas (clusters of inflamed cells) are found, a patient may be diagnosed with Crohn’s disease (CD), since these cells do not occur with UC.
  
  
• Sigmoidoscopy. Similar to a colonoscopy, but used to examine the lower portion of the large intestine (the sigmoid colon and rectum).
  
  
• Barium x-ray. X-rays of the gastrointestinal (GI) tract, after patients receive a dose of a contrast dye (barium) that allows organs to show up clearly on x-rays. Barium may be introduced to the body orally (upper GI barium tests) or via an enema (lower GI barium tests). X-rays can help identify what type of IBD is present (UC will only occur in the large intestine, whereas CD may affect any part of the digestive tract).
  
  Barium x-rays are not considered as reliable as a colonoscopy or sigmoidoscopy for diagnosing UC because the x-rays may miss polyps and do not allow tissue samples to be taken for analysis under a microscope. They are not used in case of moderate to severe UC because of the risk of complications.