Diverticulitis is usually diagnosed based on medical history, physical examination and blood tests to check for infection. Most patients display classic signs and symptoms of diverticulitis, so diagnostic imaging tests are not typically necessary. However, certain imaging tests (e.g., CAT scans, ultrasound) may be used if the diagnosis is uncertain, complications are suspected, the patient has a weakened immune system or the symptoms do not respond to medical therapy. These tests may reveal complications such as thickening of the intestinal wall, inflammation outside the colon, fistulae and abscesses.

During the evaluation of medical history, patients will typically be asked about their bowel habits, symptoms, diet and any medications they may be taking, both prescription and over-the-counter. During the physical examination, the gastroenterologist or other physician may press on the abdomen to check for fullness or tenderness and perform a digital rectal exam. This exam involves inserting a gloved, lubricated finger into the rectum to check for bleeding, blockage or tenderness. Blood tests are used to check for signs of infection. In some cases, a fecal occult blood test may be used to check for signs of intestinal bleeding.

Diagnostic imaging tests may include:

• Computed axial tomography (CAT) scan. A series of x-rays are taken from different angles to generate a three-dimensional image of the internal organs. Generally the preferred procedure when the diagnosis is uncertain or complications are suspected. A CAT scan may be assisted by a water-soluble contrast medium that may be taken orally, rectally and/or intravenously.
  
  
• Ultrasound. Sound waves are used to produce images of the internal organs. Ultrasound may be used to check for complications and rule out other possible causes of the symptoms. Ultrasound imaging may also be used to assist in draining fluid collections from outside the colon.
  
  
• Abdominal x-ray. Frequently used to rule out other possible causes of the symptoms (e.g., appendicitis). Although it is not generally recommended during a diverticulitis attack, barium may be used as a contrast medium to make the internal structures show up more clearly in these x-rays. A water-soluble contrast medium may be used instead because it is less likely to cause further irritation or inflammation.
  
  
• Colonoscopy. A tiny camera attached to a thin tube is inserted through the rectum and into the colon. It is typically not used in severe cases because it may cause rupture. However, diverticular disease may make cancer more difficult to diagnose. Because of these factors, a colonoscopy is generally performed several weeks (usually 6 to 8 weeks) after symptoms have cleared to check for any signs of colorectal cancer. The procedure may be performed at regular intervals afterward as well.
  

  

• Sigmoidoscopy. A thin tube is used to look into the rectum and sigmoid colon. In some patients, this may be used to identify whether a suspect mass is abnormal and possibly cancerous or an inflamed diverticulum.