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Crohn's Disease

How Is Crohn’s Disease Diagnosed?

To accurately diagnose Crohn’s disease, a patient will likely undergo a number of laboratory tests and one or more imaging procedures that allow a doctor to visually evaluate the intestine. Laboratory tests include blood tests and stool cultures. They are used to evaluate the inflammatory process and to provide clues about the cause. There are three common imaging procedures. One is a type of X-ray, and the others use endoscopy, allowing the doctor to actually look inside the body.

Imaging studies include:

Once transient infection has been ruled out and inflammatory bowel disease is suspected, it is important to make a correct diagnosis of either Crohn’s disease or ulcerative colitis. While the two diseases have many similarities, they are distinct. Many of the newer drugs are more effective for treating for one disease than the other.


Sigmoidoscopy is a procedure that allows the doctor to directly examine the lining of the rectum and lower portion of the colon. It is usually performed with 60-centimeter flexible fiberoptic scope, but a shorter, rigid scope may be used. The procedure can be performed in a doctor’s office or health clinic. The exam takes 5-20 minutes, and no sedation is needed.

The fiber-optic tube, which contains a light source and a camera lens, is inserted into the anus and advanced up through the rectum and into the descending (sigmoid) colon. The doctor looks for irregularities in the lining of the colon. For most people, sigmoidoscopy is mildly uncomfortable. However, for individuals who are in the midst of a flare-up of inflammatory bowel disease, the procedure can be painful.

Sigmoidoscopy is more useful for diagnosing ulcerative colitis than Crohn’s disease. The test can, however, rule out Crohn’s disease if a view of the sigmoid colon shows clear signs of ulcerative colitis.


Colonoscopy is similar to sigmoidoscopy, but the much longer colonoscope allows the doctor to thoroughly examine the entire colon (advancing from the rectum to the terminal ileum, the end of the small intestine). Modern colonoscopes use microchip-driven electronic imaging and screen projection; these have replaced older fiber-optic scopes.

Colonoscopy takes about 30 minutes and is generally performed with the patient under what is called “conscious anesthesia.” Conscious anesthesia, which can be described as a semi-conscious state, is achieved through a combination of a sedative and pain medication. Because sedation is used, colonoscopy must be performed in a hospital or an endoscopy clinic that has been approved and licensed by the state and can provide appropriate emergency care in case of anesthesia-related complications.

Because most people remain drowsy for some hours after the procedure, it is usually necessary to take the day off from work to undergo a colonoscopy.

A small set of forceps inside the colonoscope allows the doctor to remove small tissue samples for biopsy (to check for cellular changes that may indicate cancer or precancerous conditions) or to remove polyps.

Barium Enema

In this procedure, a barium sulfate suspension is injected into the colon through a tube inserted in the rectum and a series of radiographs (x-rays) is taken. Often, air is also injected to help inflate the colon. The barium suspension acts like a dye for the radiographs. Without the “dye,” plain film radiographs would not show the soft tissue of the bowel clearly. The lining of the bowel must be seen clearly if the proper diagnosis is to be made.

The barium enema is considered the “gold standard” in distinguishing among Crohn’s disease of the colon (Crohn’s colitis), Crohn’s disease of the ileum (ileitis), and ulcerative colitis. Enough barium usually goes beyond the colon into the terminal ileum to reveal if that area is diseased, and the barium allows the radiologist and the gastroenterologist to see if the disease is continuous, or skips from patches of diseased tissue to healthy tissue and back again.

Preparing For Tests

For sigmoidoscopy, preparing the bowel includes using one or two pre-mixed enemas about two hours prior to the procedure to cleanse the rectum and sigmoid colon of stool.

For colonoscopy or barium enema, the bowel preparation must completely purge the colon. Beginning on the afternoon before the exam, the patient takes one or two laxative treatments. Only clear liquids – no food or milk products – are consumed for 12 to 18 hours before the exam.

Laboratory Tests

Laboratory tests can help confirm a diagnosis of Crohn’s disease.

A blood sample drawn from a vein in the arm undergoes many tests. If disease is present, the white blood cell count may be elevated, as might the erythrocyte (red blood cell) sedimentation rate (ESR). The ESR is the rate at which blood separates into its component parts of red blood cells (which settle to the bottom of the sample vial) and plasma (which rises to the top), with other components in the middle.

A longer than normal sedimentation time (elevated ESR), combined with an elevated white cell count, signals the presence of an inflammatory process in the body. In addition, a low blood count may suggest anemia caused by malabsorption of iron, excessive internal bleeding, or chronic illness. All of these are signs of ulcerative colitis or Crohn’s disease.

As part of a rectal exam, a doctor tests to see if there is any blood in the stool smear on the glove used. This is called occult blood and signals bleeding in the intestinal tract.

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