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Diagnosing Inflammatory Bowel Disease

In inflammatory bowel disease, or IBD, there is persistent inflammation in the gastrointestinal tract. The condition causes symptoms such as abdominal pain, diarrhea, bloody stool, constipation, and an urgent need to have a bowel movement. The most common types of IBD are Crohn’s disease and ulcerative colitis.

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Gastroenterologists at NYU Langone's Inflammatory Bowel Disease Center and Inflammatory Bowel Disease Center—Long Island are experts in the gastrointestinal tract and can recommend the appropriate diagnostic tests to determine the cause of your symptoms. There is no single definitive test to confirm the presence of IBD, so the condition is diagnosed based on a combination of tests, including endoscopy, biopsy, and imaging tests.

Medical History

Your doctor asks about the symptoms you have been experiencing, when you first noticed them, how frequently they occur, how severe they are, and whether they interfere with your daily routine. In addition, he or she may ask about places you’ve traveled and whether your symptoms coincided with a trip to another country.

Your doctor may also ask about the foods you typically eat and whether your dietary habits have changed recently. Some of the symptoms of IBD may overlap with other gastrointestinal and immune conditions, such as irritable bowel syndrome, or with food sensitivities and intolerances, such as celiac disease and gluten sensitivity.

It’s also helpful to tell your doctor about any other conditions you have and whether you are taking medication for them. If you’ve had abdominal or gastrointestinal surgery, these procedures may cause symptoms similar to those of IBD. Your doctor may also ask if you have any symptoms related to an immune system abnormality, such as fever, loss of appetite, weight loss, eye irritation or blurry vision, and arthritis.

Physical Exam

Doctors conduct a physical exam to determine whether you have signs and symptoms of IBD. Your doctor may examine the abdomen, pressing gently to check for any pain or tenderness. He or she may also check to see if you have eye inflammation, mouth sores, skin rashes, joint swelling or irritation, bleeding, or other signs of inflammation in the anus and the surrounding area.

Blood Test

Although a blood test cannot confirm that you have IBD, it can help rule out conditions that cause similar symptoms. Doctors typically draw a small amount of blood, then send it to a laboratory for testing. Results are usually available in one to two days.

Blood tests can reveal several telltale signs of IBD. These include markers that indicate the immune system is causing inflammation and signs that you are anemic, meaning you have a low red blood cell count, which could be a sign of internal bleeding. Low levels of iron, folate, vitamin D, and vitamin B12 indicate a nutritional deficiency and may be a sign that the intestines are not absorbing these nutrients as they should.

Stool Test

IBD affects the frequency and consistency of bowel movements, so your doctor may ask you to provide a stool sample to be sent to a lab for testing. He or she gives you a small plastic container that you return to a specialist after you have collected a sample.

Stool tests are used to rule out infections or to assess the severity of inflammation. A stool test can also reveal the presence of blood that may not be visible to the naked eye. The results are usually available in five to seven days.

Endoscopic Procedures

Endoscopic procedures—such as colonoscopy, upper endoscopy, sigmoidoscopy, and capsule endoscopy—are key to diagnosing IBD because they provide clear and detailed views of the gastrointestinal tract. They can help doctors diagnose IBD and differentiate between Crohn’s disease and ulcerative colitis. Although these two conditions share many symptoms, they affect different parts of the gastrointestinal tract.

Your doctor decides which endoscopic test is appropriate based on your symptoms, medical history, physical exam, and the results of blood and stool tests.

Colonoscopy and Biopsy

Gastroenterologists almost always recommend a colonoscopy to diagnose Crohn’s disease or ulcerative colitis. This test provides live video images of the colon and rectum and enables the doctor to examine the intestinal lining for inflammation, ulcers, and other signs of IBD.

Frequently, a doctor performs biopsies during a colonoscopy, in which he or she removes small tissue samples from the colon and sends them to a laboratory for analysis. Biopsy results may help doctors confirm an IBD diagnosis and differentiate between Crohn’s disease and ulcerative colitis.

Before the procedure, a doctor asks you to avoid eating solid food for 24 hours. You are given a laxative solution to drink the night before so your bowels are empty during the exam.

To perform a colonoscopy, gastroenterologists use a colonoscope, a long, thin, flexible instrument with a camera and light embedded in the tip. Doctors insert the colonoscope into the anus and slowly move it through the rectum and colon. The camera displays images of the colon on a nearby computer monitor. The procedure typically takes about 30 minutes.

Before the procedure, doctors usually administer a sedative to make you sleepy and to ease any discomfort. You can return home afterward, but a friend or relative should drive because you may still feel a little drowsy.

Flexible Sigmoidoscopy

A flexible sigmoidoscopy is similar to a colonoscopy except the doctor only examines the rectum and lower part of the colon. This test may be recommended if your symptoms are limited to bleeding and inflammation around the anus and rectum. Occasionally, doctors perform this test to assess how well treatment is working. Doctors may perform a biopsy during the procedure.

Upper Endoscopy

If your symptoms and lab tests suggest that you have Crohn’s disease, your doctor may recommend an upper endoscopy, also called an esophagogastroduodenoscopy. Doctors use this procedure to examine the esophagus—the tube that connects the mouth to the stomach—as well as the stomach and first part of the small intestine. An upper endoscopy may reveal inflammation, ulcers, bleeding, or obstruction in these parts of the gastrointestinal tract.

The doctor uses a thin, flexible instrument called an endoscope to perform the test. Before the procedure, he or she gives you a sedative to make you sleepy and ease any discomfort. Then the doctor inserts the endoscope into the throat and through the esophagus and stomach to the small intestine. A camera at the tip of the device sends live images to a nearby monitor.

Doctors often take tissue samples during an upper endoscopy. Lab tests can help determine the cause of inflammation.

An upper endoscopy procedure typically takes between 10 and 20 minutes. You can return home afterward, but someone needs to give you a ride because the sedative’s effects may linger.

Capsule Endoscopy

A capsule endoscopy may be recommended if your symptoms indicate you have a problem in the small intestine but other tests—including blood tests, colonoscopy, and an upper endoscopy—are inconclusive. The small intestine is more difficult to visualize than other parts of the gastrointestinal tract because most of it is inaccessible. A capsule endoscopy may provide more detail about inflammation, ulcers, or bleeding than other tests and can help doctors determine if Crohn’s disease is causing your symptoms.

In this procedure, a doctor asks you to swallow a small capsule with a tiny camera inside. This capsule is about the size of a multivitamin. As it passes through the digestive tract, the camera takes thousands of pictures that are transmitted via radio waves to a small receiver that you wear around your waist or place in a pocket.

It takes about eight hours for the capsule to pass through the gastrointestinal tract. It is excreted through a bowel movement and flushed down the toilet. Your doctor downloads the images from the receiver, paying special attention to those that are captured in the small intestine.

Imaging Tests

When performed in combination with endoscopic tests, imaging tests—such as X-rays, CT scans, and MRI scans—give doctors additional information about the gastrointestinal tract. They can reveal signs of IBD in the lining of the intestines, such as tears, bleeding, inflammation, or an obstruction.

Often, imaging tests help doctors differentiate between Crohn’s disease and ulcerative colitis if other diagnostic tests are inconclusive. For instance, if an imaging test reveals inflammation in the small intestine, you may have Crohn’s disease, because ulcerative colitis only affects the large intestine.

Imaging tests can also be used to monitor the gastrointestinal tract and assess how well treatment is working.


X-rays use electromagnetic radiation to take pictures of the gastrointestinal tract. They are particularly useful if doctors want to determine whether symptoms such as abdominal pain and constipation are caused by an intestinal obstruction or dilation of the bowel wall.

CT Scans and CT Enterography

CT scans involve taking a series of X-rays to create detailed two- and three-dimensional images of the body. CT scans of the gastrointestinal tract can reveal a narrowing of the small or large intestine, called a stricture, or an obstruction. The test may also indicate inflammation in the small intestine, which suggests that Crohn’s disease may be causing your symptoms.

Occasionally, doctors may recommend an enhanced CT scan, known as a CT enterography. Prior to the scan, you drink a contrast agent. As the liquid passes through the digestive tract, the CT scanner takes pictures of the small intestine and may reveal anatomical problems. For example, if an obstruction is present, the contrast liquid is visibly blocked.

MRI Scans and MR Enterography

An MRI scan uses a magnetic field and radio waves to create two- and three-dimensional images of the body. MRI scans are especially helpful when doctors need to visualize soft tissues, such as the lining of the intestines. They may reveal small tears or ulcers, as well as irritation or bleeding.

To get a better look at the gastrointestinal tract, the doctor may ask you to drink a contrast agent just before the MRI. This is called MR enterography.

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