Only a medical doctor can diagnose Crohn’s disease, and there is no single test that can confirm a diagnosis. Because Crohn’s disease often presents like other health conditions, it’s important to screen for and rule out other conditions, too.
In order to diagnose Crohn’s disease, a healthcare provider will usually complete a routine physical exam and medical history assessment, in addition to ordering some or all of the following tests and measures:
- Laboratory tests
- Leukocyte scintigraphy
- Other imaging tests (CT scan, MRI, x-ray, ultrasound)
Blood tests cannot diagnose Crohn’s disease on their own, but they are important for ruling out other conditions and monitoring disease progress. Common ones ordered for people showing signs of Crohn’s disease include:
- Complete blood count (CBC), especially to check for low levels of red blood cells (anemia)
- Inflammation markers, such as C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR), which are expected to be high in inflammatory conditions like Crohn’s disease
- Liver function tests
- Electrolyte panel to measure levels of certain nutrients like potassium, which may be depleted due to excessive diarrhea
- Vitamin B-12 and other nutrient levels, which may be depleted if the small intestine can’t absorb nutrients properly
- Antibody blood tests, including perinuclear antineutrophil antibodies (pANCA) anti-saccharomyces cerevisiae antibody (ASCA), which can help distinguish Crohn’s disease from ulcerative colitis
Providers may also request and test samples of a person’s stool to look for things like blood and certain types of protein.
As part of the normal immune response, white blood cells are often highly concentrated in areas of inflammation. During a leukocyte scintigraphy, a blood sample is taken from a person’s arm, and white blood cells from the sample are tagged with a small amount of a radioactive substance. A special camera can then identify this radioactive substance, which is harmless. The surgeon then returns the blood sample to the patient’s body and the special camera detects where the white blood cells go.
Since Crohn’s disease is a chronic inflammatory disease, the condition may be to blame if many white blood cells travel to the digestive tract.
An endoscopy requires the insertion of a thin flexible tube into the digestive tract, either through the anus or through the mouth. The end of the tube contains a small camera to allow doctors to see inside the digestive tract. A person is sedated during this procedure for their comfort and may be asked not to eat or drink for a certain period of time beforehand.
There are several different types of endoscopic procedures that doctors may order:
- Sigmoidoscopy allows doctors to examine the lower part of the large intestine
- Colonoscopy allows doctors to examine the entire colon and sometimes the very end of the ileum
- Esophagogastroduodenoscopy (EGD) allows doctors to examine the uppermost part of the digestive tract, including the esophagus, stomach, and duodenum
- Chromoendoscopy is performed during a colonoscopy; doctors spray a blue liquid dye into the colon to highlight and abnormalities in the lining of the intestines, including polyps and precancerous tissue
- Capsule endoscopy uses a miniature camera placed inside a pill-sized capsule that the person swallows; as it passes through the digestive tract, the camera inside the capsule takes up to 50,000 images, many of which can’t be seen on normal endoscopic procedures—these images are transmitted to a recording device and then a person passes the capsule in their stool
- Endoscopic retrograde cholangiopancreatography (ERCP) allows doctors to look at the pancreatic ducts and liver bile ducts
Other Imaging Tests (CT Scan, MRI, Ultrasound)
Many types of imaging technology can be used to diagnose and monitor Crohn’s disease, in addition to endoscopic procedures. Since endoscopic procedures are more invasive, many of these other imaging tests are used first. They include:
- Computerized tomography (CT) scan: CT scans (also called CAT scans) take multiple simultaneous X-ray images from different angles to create many cross-sectional images of the targeted body area (like slices of bread)
- Magnetic resonance imaging (MRI) scan: MRI technology uses magnetic energy and radio waves to create images of organs and tissues; research suggests MRI may be useful for detecting inflammation, fistulas, and abscesses in people with this disease
When used for Crohn’s disease, these procedures are sometimes called enterography or enteroclysis (e.g., CT enterography or MR enterography).
Endoscopic ultrasound (EUS) is a new procedure that uses a small ultrasound device (instead of a camera) attached to the end of an endoscopic probe. Ultrasound technology emits sound waves against tissues and then transforms these waves into images on a screen. EUS is commonly used to look for fistulas near the rectal area. Ultrasound can sometimes be used “transabdominally,” in which the probe is passed over the lower part of the stomach instead of being inserted into the person’s body.
A biopsy is the removal of a small piece of tissue that experts then test and analyze in a lab. Doctors often perform biopsies of intestinal tissue to assess for issues like inflammation and to rule out other conditions. Biopsies occur during an endoscopic procedure, so doctors can see where they are making small incisions.
Is Crohn’s disease hard to diagnose?
Crohn’s disease can be hard to diagnose, and it may take months for a person and their healthcare provider to know what’s causing their symptoms. This delay in diagnosis is for several reasons.
First, many of the signs and symptoms of Crohn’s disease can present like a number of other health conditions. This means providers usually need to rule out other conditions before they can make an accurate Crohn’s diagnosis. Second, there is no one specific test that can confirm a diagnosis of Crohn’s disease. Third, Crohn’s disease can present differently from person to person, so healthcare providers may need to do a different combination of tests depending on each patient’s presentation, health status, and other factors.
Can Crohn’s disease be detected by a blood test?
Crohn’s disease can’t be confirmed by blood tests alone. But blood tests are an important part of the diagnostic process because they help rule out other conditions, assist in making a diagnosis, and monitor the progress of the disease. So, blood and stool tests always need to be accompanied by other tests to help confirm a Crohn’s diagnosis and distinguish it from ulcerative colitis.