Diagnosing Crohn's Disease

Medically Reviewed by Minesh Khatri, MD on August 12, 2022
6 min read

There isn't any single test that can diagnose Crohn's disease. This condition has many symptoms that are the same as those for other health problems.

To make a diagnosis of Crohn's disease, your doctor is likely to gather information from multiple sources. You'll probably go through a combination of exams, lab tests, and imaging studies with these goals in mind:

  • Rule out other health problems
  • Make a clear diagnosis of Crohn's disease
  • Find out exactly which part of the digestive tract is affected

In general, your primary care doctor will do an initial physical exam, take your health history, and do some lab tests to start to zero in on a diagnosis. If they suspect Crohn’s, they’ll send you to a doctor called a gastroenterologist that specializes in Crohn’s disease and other conditions of the gastrointestinal, or “GI,” tract.

Your gastroenterologist is typically the one who does more in-depth exams to get images and other information about the inside of your body. This may include a colonoscopy that takes video and collects tissue samples (biopsies), along with imaging like barium x-ray or MRI, and other tests your GI doctor thinks helpful.

Your doctor will begin by gathering information about your health and your family health history. They’ll do a physical exam and look for symptoms of Crohn’s that usually include:

  • Belly pain and cramps
  • Blood in your poop
  • Diarrhea
  • Drainage from a painful sore near your anus
  • Fatigue
  • Fever
  • Lack of appetite
  • Mouth sores
  • Urgent bowel movements
  • Weight loss

Your doctor may request lab tests in order to look for problems that might be linked to Crohn's disease. These tests check for signs of infection, inflammation, internal bleeding, and low levels of substances such as iron, protein, or minerals.

Blood tests may include:

  • Antibody tests: These help doctors tell if you have Crohn’s or ulcerative colitis:
    • Anti-Saccharomyces cerevisiae antibody test (ASCA): People with this protein are more likely to have Crohn’s.
    • Perinuclear anti-neutrophil cytoplasmic antibody test (pANCA): People with this protein are more likely to have ulcerative colitis.
  • Complete blood count (CBC): It checks for anemia (low numbers of red blood cells) and infection.
  • C-reactiveprotein: It looks for this protein, which is a sign of inflammation.
  • Electrolyte panel: Your body might be low on minerals like potassium if you have Crohn’s-related diarrhea.
  • Erythrocyte sedimentation rate: This gauges the amount of inflammation in your system by measuring the amount of time it takes for your blood to fall to the bottom of a special tube.
  • Iron and B12 levels: These can be low if your small intestine isn’t absorbing nutrients like it should.
  • Kidney function.
  • Liver function: The disease can affect your liver and bile duct.

Crohn's disease may appear anywhere along the gastrointestinal tract, from the mouth to the rectum. X-rays and other images can help identify the severity and location of Crohn's disease. These studies may include the following:

Balloon-assisted enteroscopy: There are about 20 feet of small intestines in your body. They curve around and lie on top of one another. This test makes it easier for doctors to look at them. The version most often used for Crohn’s is a double-balloon (or double-balloon assisted) test. There’s also a version with a single balloon. Both types work like this: The doctor uses a special flexible tube called an endoscope, which has a tiny camera on one end. It has either one or two balloons attached behind it. They’ll inflate them and deflate the balloons to move the tube through your intestine. It’s a lot like pulling a curtain onto a rod.

Barium X-rays and other X-rays: A barium X-ray can show where and how severe Crohn's disease is. It is especially helpful for finding any problems in parts of the small intestine that can't be easily viewed by other techniques.

A chalky fluid containing barium is given by mouth or through the rectum. When barium fluid is given by mouth, it is called an upper GI series. When barium fluid is placed in the rectum, it is called a barium enema. The barium fluid flows through your intestines and looks white on X-ray film. This makes it easier to view problem areas. With a barium X-ray, your doctor may be able to see ulcers, narrowed areas of the intestine, abnormal connections between organs, known as fistulae, or other problems.

If barium X-rays show some sign of disease, your doctor may request other X-rays or imaging studies. These X-rays can help identify exactly how much of your digestive tract is affected by Crohn's disease.

Colonoscopy or sigmoidoscopy: Colonoscopy and sigmoidoscopy allow your doctor to directly view the large intestine, which is the lower part of the digestive tract. These techniques can often provide the most accurate information about the intestines. They may be better at finding small ulcers or inflammation than other techniques. They can be used to judge the severity of any inflammation. Colonoscopy is the most important tool in diagnosing Crohn's disease.

During these procedures, a flexible viewing tube is placed through the anus into the large intestine. An image of the inside of the intestine is often projected onto a video monitor. A sigmoidoscopy involves examining the lowest part of the large intestine. A colonoscopy can provide a view of all of the large intestine and often the end of the small intestine, which is frequently affected by Crohn's. In either case, the doctor can directly view the colon to check for signs of ulcers, inflammation, or bleeding. The doctor can also take small samples of tissue to examine under a microscope, known as a biopsy. This helps determine whether the tissue shows signs of Crohn's disease or other problems.

Computed tomography (CT) scan: CT scanning uses computer-aided X-ray techniques to make more detailed images of the abdomen and pelvis than can be seen in traditional X-rays. CT scans can help find abscesses that might not show up on other X-rays. Abscesses are small pockets of infection.

Leukocyte scintigraphy: White blood cells gather at spots in your body where there’s inflammation. For this test, the doctor will take a little blood from your arm and add a harmless amount of a radioactive substance. They’ll put it back in your body and use a special camera to see if the cells travel to spots in your gastrointestinal tract that could signal Crohn’s. It’s not a commonly used test.

Magnetic resonance imaging (MRI): Use of MRI to make a Crohn’s diagnosis is on the rise. This test gives your doctor a clear picture of the inside of your body, but it doesn’t subject you to radiation. It can help your doctor see your small intestines and spot an anal abscess (pus-filled sore) or fistula (tunnel that forms between an abscess and one of your anal glands). When you get this test, you’ll lie on a table that slides into a machine, so let your doctor know if you have a problem with enclosed spaces.

Video capsule endoscopy: For video capsule endoscopy, you swallow a small capsule or pill that holds a miniature video camera. As it travels through your small intestine, it sends images of the lining to a receiver you wear on a belt around your waist. The doctor downloads the images and reviews them on a computer. They can provide detailed information about early, mild problems associated with Crohn's disease. This technique may be especially helpful if you have symptoms of Crohn's disease that can’t be seen by other small bowel tests.

While video endoscopy can provide valuable information, it won’t work for everyone. You should avoid it if:

  • You have an obstruction in the small intestine. The capsule could get stuck and make the obstruction worse.
  • You have a narrowing in the small intestine, such as from Crohn's disease, previous surgery, or previous radiation therapy. The capsule might become stuck.
  • You have an implanted device like a pacemaker or defibrillator for your heart. Some doctors worry that wireless transmissions from the capsule might interfere with them.

After the exams, lab tests, and imaging tests are done, your doctor will discuss the findings with you. If your doctor believes you have Crohn's disease, then you can work together to develop a treatment plan to manage the symptoms and control the disease.