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The diagnosis of Crohn's disease can sometimes be challenging, and a number of tests are often required to assist the physician in making the diagnosis. Sometimes even with all the tests the Crohn's does not show itself. A colonoscopy has about a 70% chance of showing the disease and the rest of the tests go down in percentage. Disease in the small bowel can not be seen through some of the regular tests; for example, a colonoscopy can't get there.
Endoscopy
A colonoscopy is the best test for making the diagnosis of Crohn's disease as it allows direct visualization of the colon and the terminal ileum, identifying the pattern of disease involvement. Occasionally, the colonoscope can travel past the terminal ileum but it varies from patient to patient. During the procedure, the gastroenterologist can also perform a biopsy, taking small samples of tissue for laboratory analysis which may help confirm a diagnosis. As 30% of Crohn's disease involves only the ileum, cannulation of the terminal ileum is required in making the diagnosis. Finding a patchy distribution of disease, with involvement of the colon or ileum but not the rectum, is suggestive of Crohn's disease, as are other endoscopic stigmata.
Wireless capsule endoscopy is a technique where a small capsule with a built-in camera is swallowed, the camera takes serial pictures of the entire gastrointestinal tract and is passed in the patient's faeces. It has been used in the search for Crohn's disease in the small bowel, which cannot be reached with colonoscopy or gastroscopy.The utility of capsule endoscopy for this, however, is still uncertain.
Radiologic tests
A small bowel follow-through may suggest the diagnosis of Crohn's disease and is useful when the disease involves only the small intestine. Because colonoscopy and gastroscopy allow direct visualization of only the terminal ileum and beginning of the duodenum, they cannot be used to evaluate the remainder of the small intestine. As a result, a barium follow-through x-ray, wherein barium sulfate suspension is ingested and fluoroscopic images of the bowel are taken over time, is useful for looking for inflammation and narrowing of the small bowel. Barium enemas, in which barium is inserted into the rectum and fluoroscopy used to image the bowel, are rarely used in the work-up of Crohn's disease due to the advent of colonoscopy. They remain useful for identifying anatomical abnormalities when strictures of the colon are too small for a colonoscope to pass through, or in the detection of colonic fistulae.
CT and MRI scans are useful for evaluating the small bowel with enteroclysis protocols.They are additionally useful for looking for intra-abdominal complications of Crohn's disease such as abscesses, small bowel obstruction, or fistulae. Magnetic resonance imaging (MRI) are another option for imaging the small bowel as well as looking for complications, though it is more expensive and less readily available
Blood tests
A complete blood count may reveal anemia, which may be caused either by blood loss or vitamin B12 deficiency. The latter may be seen with ileitis because vitamin B12 is absorbed in the ileum. Erythrocyte sedimentation rate, or ESR, and C-reactive protein measurements can also be useful to gauge the degree of inflammation.[41] Testing for anti-Saccharomyces cerevisiae antibodies (ASCA) and anti-neutrophil cytoplasmic antibodies (ANCA) has been evaluated to identify inflammatory diseases of the intestine and to differentiate Crohn's disease from ulcerative colitis.
[edit] Comparison with ulcerative colitis
The most common disease that mimics the symptoms of Crohn's disease is ulcerative colitis, as both are inflammatory bowel diseases that can affect the colon with similar symptoms. It is important to differentiate these diseases, since the course of the diseases and treatments may be different. In some cases, however, it may not be possible to tell the difference, in which case the disease is classified as indeterminate colitis.
Comparisons of various factors in Crohn's disease and ulcerative colitis Crohn's disease Ulcerative colitis
Terminal ileum involvement Commonly Never
Colon involvement Usually Always
Rectum involvement Seldom Usually
Involvement around the anus Common Seldom
Bile duct involvement Lower rate of primary sclerosing cholangitis Higher rate
Distribution of Disease Patchy areas of inflammation Continuous area of inflammation
Endoscopy Deep geographic and serpiginous (snake-like) ulcers Continuous ulcer
Depth of inflammation May be transmural, deep into tissues Shallow, mucosal
Fistulae Common Seldom
Stenosis Common Seldom
Autoimmune disease Widely regarded as an autoimmune disease No consensus
Cytokine response Associated with Th1 Vaguely associated with Th2
Granulomas on biopsy Can have granulomas Granulomas uncommon
Surgical cure Often returns following removal of affected part Usually cured by removal of colon
Smoking Higher risk for smokers Lower risk for smokers
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