is quite low, particularly when symptoms have been going on for many weeks or even months, it is important to rule out infections before embarking on many types of therapy for Crohn’s disease and ulcerative colitis.
Stool may also be examined for parasites or the eggs of parasites. Occasionally, the laboratory will report that no parasites were seen, but that many white blood cells are present in the stool. The presence of white blood cells almost always indicates some type of inflammatory condition in the intestine. Stool can also be tested for certain proteins — calprotectin and lactoferrin — that are present in white blood cells that indicate the presence of active intestinal inflammation. The calprotectin level in stool has proven to be quite useful in people who present with symptoms that are not clearly or highly likely to be due to IBD. In that situation, an elevated calprotectin level is very suggestive of an underlying inflammatory condition such as IBD, and would support going ahead with other testing, such as endoscopy and biopsy, that can confirm the diagnosis.
Disease Activity
Stool tests can be used to monitor disease activity and response to treatment. These tests, when combined with blood tests, help make decisions regarding changes in treatment strategies.
X-Rays
Since the intestine does not appear in sufficient detail on plain X-rays, a contrast agent, usually barium, is used to fill the intestine so that the intestinal lining and wall can be seen in contrast to the barium. The barium is administered in several ways, depending on the area of bowel under examination. Because of the two-dimensional limitation of these techniques, they have been largely replaced by cross-sectional imaging studies, such as ultrasound, CT scan, and MRI.
Upper GI Series and Small Bowel Follow-Through
When examining the small intestine, the barium can be given by having the person drink it. X-rays are taken every few minutes as the barium passes out of the stomach and through the small intestine. This type of X-ray can also detect problems in the esophagus, stomach, and duodenum. It requires no preparation on the part of the patient other than having to fast on the day of the examination.
Small-Bowel Enema, or Enteroclysis
In some cases, a small-bowel follow-through X-ray doesn’t provide enough detail because of problems with the movement of barium through the small intestine or because the images are captured only every few minutes and important information can be missed. To solve this problem, the barium is administered directly into the small intestine by means of a tube placed through the nose into the esophagus, stomach, and duodenum. The radiologist can watch continuously as the barium flows through the entire small intestine. This examination also requires only fasting prior to the procedure.
Barium Enema
Barium enema provides images of the large intestine (colon). Liquid barium solution and air are pumped into the large intestine. A barium enema is rarely performed, however, having been replaced by colonoscopy and CT scan. Conversely, a normal calprotectin level makes the likelihood of IBD much lower, and the doctor and patient or family may then decide against further testing. This decision can be of value when it comes to children, for whom a test such as endoscopy is more difficult to do.
X-Ray Risk
All X-rays involve some degree of exposure to radiation, but, as long as the tests are not repeated frequently, the amount of radiation exposure is relatively small compared to the amount that one is exposed to every day from background sources.
Imaging Studies
Imaging studies provide “pictures” of the intestines and other internal organs without having to open up the abdomen by performing surgery. Imaging studies have been the mainstay of IBD diagnosis for many years. X-rays provide two-dimensional pictures of the intestine, while other types of imaging studies also provide information about surrounding structures within the abdomen, something which conventional X-ray studies cannot do. These include ultrasounds, computer-assisted tomography (CT, or CAT) scans, and magnetic resonance imaging (MRI). They provide multiple images of the abdomen in “slices” that can be positioned crosswise or lengthwise through the abdomen. In this way, it is possible to provide a three-dimensional representation of the intestines, other abdominal organs, and even blood vessels. Because of this capability, these imaging studies can provide improved diagnostic information compared with conventional X-ray studies.
Ultrasound
Ultrasound examinations are very safe and widely available. A probe that transmits a high-frequency sound wave is moved over the abdominal wall. That sound wave is reflected off structures within the abdomen and back to the probe, which has a sensor to detect the reflected sound waves, or echoes. These echoes are then converted into an image. Patients must fast before an abdominal ultrasound study. There are certain modifications of the ultrasound technique that can allow the radiologist to determine the rate of blood flow within the intestine. An increased blood flow may give an indication that the bowel is inflamed.
One particular type of ultrasound, a transanal ultrasound, is used to evaluate patients for possible anal abscesses and fistulas. This involves putting a special ultrasound probe into the anus in order to obtain images of the surrounding tissues. Although this may provide excellent detail, the procedure may be very difficult or impossible for patients with painful anal conditions associated with Crohn’s disease.
Detecting Complications
Ultrasound may be helpful in detecting complications of IBD, such as abscesses, but it is not the most sensitive imaging study, particularly when the intestines are to be evaluated.
Computer-Assisted Tomography (CAT scan, or CT scan)
Computer-assisted tomography is a very safe and widely used imaging technique. This technology, along with MRI, has virtually replaced the small bowel follow-through and small-bowel enema procedures.
During a CT scan, the patient lies on a table, which is surrounded by a large donut-shaped structure that produces and detects X-rays. These X-rays are converted into very detailed images when processed in the machine’s computer.
Patients undergoing CT scans of the abdomen are often given a contrast solution to drink 1 to 2 hours before the scan to provide better diagnostic images or an intravenous injection of another contrast material to show blood supply to the intestine and other tissues.
CT scans are generally not needed for routine follow-up of a patient’s clinical disease activity. If an abscess is detected by CT scan, the images can be used by the radiologist to insert a needle or plastic tube through the skin and into the abscess in order to allow it to drain properly.
CT scans involve radiation exposure, which is always a concern, particularly in young people. However, newer “low-dose” CT scans expose patients to a fraction of the radiation that they would be exposed to with a standard CT scan, without losing much of the important diagnostic information.
Sensitive Test
CT scans are very sensitive at detecting IBD complications, such as abscesses and intestinal obstructions. They do involve some radiation exposure and so should not be repeated too frequently or unnecessarily.
Magnetic Resonance Imaging (MRI)
Magnetic
