Crohn's Disease Tests
Updated on 6/4/09
Crohn's disease may be difficult to diagnosis or evaluate with only a standard yearly physical examination. Initially, the only evidence of the disease may be a low-grade fever, joint pain, or anemia along with abdominal pain, nausea, or diarrhea—although some people are diagnosed when they're in so much pain they're in the emergency room. A combination of blood tests, stool studies, radiologic imaging tests, and endoscopic procedures are often used to make a diagnosis of Crohn's disease, assess disease activity, and evaluate patients for complications.
A CBC (complete blood count) is often taken to evaluate for anemia, signs of infection, or side effects to medications. The two most common types of anemia found in patients with Crohn's disease are due to iron deficiency and vitamin B12 deficiency. Because of severe diarrhea or vomiting, electrolyte levels may be abnormal. An elevated C-reactive protein and a high red cell sedimentation rate are markers of systemic inflammation, infection, or other illnesses. Abnormal liver function tests may indicate liver or bile duct abnormalities or a side effect of medications. Because patients often present with diarrhea, stool studies are often checked to evaluate for treatable intestinal infections that may be contributing to symptoms.
Antibody testing may be useful in patients with "indeterminant colitis," in which the diagnosis of Crohn's disease or ulcerative colitis is uncertain. The two most common antibody tests are the ASCA (anti-Saccharomyces cerevisiae antibody) and pANCA (perinuclear anti-neutrophil cytoplasmic antibody) tests. Patients with Crohn's disease are often positive for ASCA but negative for pANCA. The opposite is often true for ulcerative colitis. While the tests are not perfectly reliable, results may help guide medical and surgical management of inflammatory bowel disease.
If a physician sees a patient suffering from frequent diarrhea or occasional abdominal cramps, and the person's laboratory values give cause for concern, generally the next step is to evaluate the patient's gastrointestinal tract. This section contains more on the two types of tests used:
Imaging tests
Plain abdominal X-rays are often performed on patients with Crohn's disease, who can have intestinal narrowing that leads to small bowel obstruction. The problem can be seen on abdominal X-rays as dilated loops of small intestine or fluid-filled loops of small intestine.
This section also contains information on:
Barium enema
The barium enema is a useful diagnostic tool for evaluation of patients with Crohn's disease. It shows the right colon and the terminal part of the ileum (the final three fifths of the small intestine), the areas most often involved in Crohn's disease.
During this test, barium—a white, chalky liquid—is administered through a rectal tube. The colon fills up and is visualized with an X-ray or fluoroscope. Air is introduced into the colon until it is fully distended and coated with barium. Spot films are taken during the filling of the colon and a series of overhead films are taken after the patient has been positioned to allow viewing of the entire colon.
The physician looks for aphthous ulcers, seen as small filling defects with an opaque center; loss of detail in the lining; cobblestone defects; segmented areas damaged by inflammation; fistulas, or abnormal passages from the intestines to adjacent organs; an asymmetric appearance; and narrowing of the bowel. The test has been used for many years and is considered very safe.
Small bowel series
For this test, the patient drinks a barium liquid. Abdominal radiographs are taken at 20- to-30 minute intervals. When the barium reaches the right colon, X-rays are taken with the patient in various positions. Small bowel X-rays reveal the extent of disease, narrowing or constricting of the bowel, and partial obstructions. This is a fast, safe test for Crohn's disease.
In a related test, an enteroclysis, a patient is mildly sedated and then a tube is passed through the nose and advanced through the stomach into the small intestine.Under fluoroscopic imaging, barium is infused through the tube with a methylcellulose solution, resulting in distention and coating of the small intestine loops. This test is considered much more sensitive for very localized lesions but is much more technically difficult.
Computed tomography (CT)
CT scanning is a valuable tool to evaluate the extent of disease in patients with Crohn's disease. It is complementary to contrast examinations, like the barium enema and small bowel series. During the test, a series of X-rays are taken by a machine that encircles the body like a giant tube. Computers are used to generate cross-sectional images of the insides of the body.
The CT scan can reveal details in lining and walls of organs. The stomach, small intestine, and colon can all be visualized. CT scans are especially useful for detecting bowel inflammation, intestinal strictures and fistulas, intestinal obstruction, intra-abdominal abscesses, and perforations.
Magnetic resonance imaging (MRI)
MRI is a technique that measures the response of atoms in the body to a strong magnetic field. The response is then converted into an image of the body. Older MRI machines required the patient to lie inside an enclosed MRI scanner. Newer MRI machines have a more "open," less claustrophobic setup.
MRI is particularly useful in evaluating perianal disease. The MRI is very sensitive in evaluating for perianal fistulas and abscesses. In addition, a magnetic resonance cholangiopancreatography (MRCP), a specialized MRI to image the liver, pancreas, and bile ducts, may be used in Crohn's disease patients with abnormal liver function tests where primary sclerosing cholangitis is suspected.
Endoscopic tests
Endoscopy is important at the time of initial diagnosis to determine the inflammatory damage. During endoscopy, the doctor uses a flexible lighted tube (endoscope) with a camera inside, which projects images to a video monitor. Endoscopic tests may also be used to evaluate progression of the disease and to watch for signs of abnormal changes in cells or possible colon cancer.
This section contains more information on:
- Flexible sigmoidoscopy
- Colonoscopy
- Esophagogastroduodenoscopy (EGD)
- Capsule endoscopy and endoscopic retrograde cholangiopancreatography (ERCP)
Flexible sigmoidoscopy
This test is a simple office procedure that takes only 10 to 20 minutes. Since the colon must be clear of stool to ensure visibility, the patient undergoes a preparation that may include a liquid diet, enema, and laxatives the day before the exam. The doctor inserts the sigmoidoscope through the rectum into the lower portion of the large intestine, the sigmoid colon. Images from inside the lower part of the colon are projected on a video screen, allowing the doctor to view any ulcers, bleeding, or lesions. Biopsy forceps may be inserted through a channel in the scope to removea small tissue sample for microscopic examination. Sometimes it is necessary for the doctor to introduce air into the colon to improve visibility. Most patients feel discomfort.
The test shows only the lower one third of the colon. It is used to assess the severity of disease in that area, the source of bleeding, and the presence of intestinal infections that may be contributing to the patient's symptoms.
Colonoscopy
This procedure usually takes 30 to 60 minutes and can be done in an office or a hospital. It allows the physician to see the rectum, the entire colon, and the terminal ileum (the end of the small intestine). The colon must be completely empty to do the exam. Generally, patients are placed on a liquid diet for a day or two and given oral laxatives or enemas to clear the colon. Sedation is administered so the patient does not experience major discomfort.
During the exam, the physician inserts a long, flexible lighted colonoscope into the rectum and guides it through the colon. The colonoscope transmits images from inside the colon to a video monitor. Air may be infused into the colon to enhance visibility. During the test, a variety of instruments can be used through a biopsy channel in the colonoscope to obtain tissue samples.
A colonoscopy is useful for obtaining biopsies in the evaluation and confirmation of Crohn's disease of the terminal ileum. It is useful for visualizing and obtaining biopsies of the colon to evaluate for Crohn's colitis and distinguish it from ulcerativecolitis. Furthermore, since patients with Crohn's colitis and ulcerative colitis have an increased risk of developing colon cancer, a colonoscopy is used to obtain biopsies of the colon to screen patients for dysplasia, microscopic changes in the colon that can lead to cancer. In patients who have had Crohn's for eight to 10 years, a colonoscopy to screen for cancer every two to three years is recommended. Those with Crohn's for 20 years should have a colonoscopy at one- to two-year intervals.
Esophagogastroduodenoscopy (EGD)
An EGD usually takes 10 to 20 minutes and can be done in an office or a hospital. It allows the physician to see the esophagus, stomach, and first part of the small intestine. Generally, patients are told not to eat or drink anything after midnight on the day of the procedure. Sedation is administered so the patient does not experience major discomfort.
During the exam, the physician inserts a long flexible, lighted endoscope into the mouth and guides it down the esophagus and into the stomach and small intestine. Air may be infused to enhance visibility. The endoscope transmits images to a video monitor. During the test, a variety of instruments can be used thorough a biopsy channel to obtain tissue.
While the EGD visualizes only a small portion of the small intestine, it is particularly important in patients with suspected upper gastrointestinal tract Crohn's disease, involving the esophagus, stomach, and first part of the small intestine.
Capsule endoscopy and endoscopic retrograde cholangiopancreatography (ERCP)
Two other procedures may be used in Crohn's disease patients. A capsule endoscopy involves swallowing a camera enclosed in a capsule that sends images to a recorder belt that the patient wears. The capsule endoscope sends continuous images to the recorder as it passes through the small intestine and into the colon, then is excreted with the stool. Several studies have demonstrated that the capsule endoscope is very good at diagnosing small intestinal Crohn's disease. However, the capsule endoscope should not be used in patients with stricturing Crohn's disease or any evidence of bowel obstruction.
An ERCP combines X-ray and endoscopy to look at the bile ducts and pancreatic ducts. This technique is used in patients with abnormal liver function tests in which the diagnosis of primary sclerosing cholangitis is suspected. It may also be useful in Crohn's disease patients with gallstone disease in which gallstones get lodged in the bile ducts.
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