A bowel obstruction may be diagnosed by a physician during a physical examination that includes a medical history. Patients may also be referred to a gastroenterologist (a physician that specializes in the function and disorders of the digestive system).

During the physical examination, the physician may press on the abdomen to check for fullness or tenderness, and may use a stethoscope to listen for sounds in the intestines. A physician may also perform a digital rectal exam. This exam involves inserting a gloved, lubricated finger into the rectum to check for bleeding, blockage or tenderness. 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 nonprescription. Blood tests and urinalysis will usually be ordered to rule out infection and check electrolyte levels.

The symptoms of bowel obstruction and other gastrointestinal conditions, especially intestinal pseudo obstruction (causes similar symptoms, but no obstruction can be found), are very similar. Because of this, the diagnosis of bowel obstruction occurs only after imaging tests are performed. Depending on the suspected location of the obstruction (small or large intestine) these may include:

• X-ray. An image may be taken of the chest and abdomen on film paper or fluorescent screens. It is produced by using low doses of radiation. X-rays may show dilated loops of intestine that indicate the location of the obstruction. These images may also show air around the intestine or under the diaphragm. Air, which is not normally found in these areas, is a sign of a ruptured intestine, which will require immediate medical treatment.
  
  
• Computed axial tomography (CAT) . A test that allows for multiple x-rays to be taken from different angles around the patient. It creates images of organs and bones within the body. A CAT scan is useful in detecting if strangulation is present (when blood supply to the small intestine is impaired).
  
  
• Endoscopy. A diagnostic exam in which a tube containing an optical camera (endoscope) is fed through the mouth, passing though the esophagus into the stomach. This exam allows a physician to view the inside of hollow organs or body cavities and locate the obstruction site.
  
  
• Upper GI series. A test in which an x-ray is taken after the patient ingests liquid barium. Typically, images are taken of the stomach along with the esophagus, duodenum or both. An upper GI series can reveal the cause of obstruction to the small intestine, but is not performed when a large intestine obstruction is suspected.
  
  
• Colonoscopy. If a physician suspects blockage in the colon, this exam may be ordered. During a colonoscopy, a physician uses a long, slender tube attached to a video camera and monitor (called a colonoscope). The tube is inserted in the patient’s rectum and guided up through the colon, which allows the physician to view the patient’s entire colon and rectum.
  
  If the obstruction is caused by a volvulus (abnormal twisting of a segment of the intestine around itself), a physician can use the colonoscope not only to confirm a diagnosis, but also to attempt to untwist the intestine and relieve the obstruction. The procedure takes 15 minutes to an hour and requires a sedative. In rare cases, though, a colonoscopy may cause bleeding or perforation of the colon wall.
  
  
• Lower GI series. During this type of x-ray testing, a chemical compound containing barium is administered into a patient’s rectum via a tube (enema). The barium outlines the colon and rectum, which can help reveal the cause of a large intestine obstruction.