From Amber J. Tresca,
Your Guide to Inflammatory Bowel Disease (IBD).
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About.com Health's Disease and Condition content is reviewed by Kate Grossman, MD

When inflammatory bowel disease (IBD) is suspected based on symptoms and history, a series of tests may be used to confirm the diagnosis. In some situations, IBD may be suspected, but other causes for symptoms must be ruled out first through diagnostic tests. In some cases where IBD is the working diagnosis, it may be difficult to distinguish which form of IBD (either Crohn’s disease or ulcerative colitis) is present. More tests, or watchful waiting, may be used to help distinguish the form of IBD.

The first clue in the diagnosis of IBD are the symptoms:

• Unrelenting diarrhea
• Blood or mucus in the stool (more common with ulcerative colitis than Crohn’s disease)
• Fever
• Abdominal pain

However, some of these symptoms may also be present with a parasitic infection, diverticulitis, celiac disease, colon cancer, or other less common conditions. With this in mind, IBD may not be the most likely disorder that a gastroenterologist has in his list of differential diagnoses (the list of possible diseases that fit the symptoms).

The first tests that may be done are blood tests and a stool test. The blood tests may include a complete blood cell (CBC) count, electrolyte panel, and liver function tests (LFT).

• The CBC count can include a check of the white blood cell (WBC) count and the red blood cell (RBC) count. A high WBC count may indicate that there is inflammation somewhere in the body. A low RBC count could indicate that there is bleeding (if not obvious from visible blood in the stool) or show how much blood has been lost.
• An electrolyte panel measures the level of sodium, potassium, chloride, and carbon dioxide in the body. Chronic diarrhea may cause electrolytes abnormalities.
• LFTs measure alanine transaminase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP), albumin, total protein, and total and direct bilirubin levels. Abnormal levels may be caused by malnutrition because the gastrointestinal tract is not absorbing nutrients as it should.
• A fecal occult blood test (also called stool gaiac or hemoccult test) is used to examine stool for traces of blood that can not be seen with the naked eye. Stool can also be tested for the presence of a bacterial infection that could cause symptoms.

A gastroenterologist may wait for the results of these tests before proceeding to other tests such as radiology (X-rays) or endoscopic procedures (colonoscopy or sigmoidoscopy). If the symptoms are severe, and a patient is in distress or severely ill, a gastroenterologist may not wait before ordering more tests.

• X-rays are quick, cheap, non-invasive, and an X-ray of the abdomen can show if the bowel is narrowed, obstructed, or dilated.
• Barium enema (also called a lower gastrointestinal series) is a special type of X-ray that uses barium sulfate and air to outline the lining of the rectum and colon. The results can show polyps, tumors, or diverticulosis.
• An upper gastrointestinal (upper GI) series is a type of X-rays used to examine the esophagus, stomach, and duodenum (the first section of the small intestine). Sometimes it is used to examine the small intestine.
• A sigmoidoscopy is an endoscopic procedure that is used to examine the last third of the large intestine, which includes the rectum and sigmoid colon. This test can be used to check for cancer, abnormal growths (polyps), inflammation, and ulcers.
• A colonoscopy is an endoscopic procedure used to examine the inside of the colon which can go beyond the areas a sigmoidoscopy can reach. A colonoscopy is useful in detecting colon cancer, ulcers, inflammation, and other problems in the colon. Biopsies can also be taken during a colonoscopy and examined for clues in making a diagnosis.
• An upper endoscopy is used to see inside the esophagus, stomach, and duodenum (first section of the small intestine). It may be used to find the source of swallowing problems, nausea, vomiting, reflux, bleeding, indigestion, abdominal pain, or chest pain.

Depending on the symptoms and the suspected cause of the problem, a combination of these tests may be ordered. Each test has advantages and disadvantages, and a physician will use the information gleaned from a patient's history (such as severity and duration of symptoms and family history) to order the tests that will be most effective in determining the cause of the symptoms. The test results themselves will be examined to see if they fit with a diagnosis of a form of IBD, or if there might be another cause of the symptoms.

_Sources:

Velayos F, Mahadevan, U. "How IBD Is Diagnosed." Crohn's and Colitis Foundation of America 2008. 09 Apr 2008.

Cleveland Clinic. "Inflammatory Bowel Disease." ClevelandClinic.org 2008. 09 Apr 2008.

Division of Gastroenterology. "Diagnosis & Treatment of Inflammatory Bowel Disease." University of California, San Diego 2006. 09 Apr 2008.