Chapter 06 · Diagnosis

Diagnostic Tests Explained

Not sure what to expect during an imaging exam or endoscopy? Here’s a clear, step-by-step guide to the most common procedures in Crohn’s disease.

Diagnosing Crohn’s disease usually involves several tests, and some may be ones you’ve never had before. Here are the most common diagnostic procedures in Crohn’s disease, explained simply.

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CT Scan

Using X-ray beams to create detailed pictures of your body

Physicians may order a CT scan to examine parts inside your body, including soft tissues like organs, but also bones, blood vessels, or even the brain. A CT scan uses X-ray beams to create pictures. The scan can take up to 30 minutes and isn’t painful at all. In some cases, you might need an IV (a small tube inserted into your vein) before the scan starts, as you’ll receive a contrast agent that helps differentiate different soft tissues.

📋 For the exam

You’ll lie on a comfortable table with a blanket.
The table will slowly move into a large, round machine (shaped like a donut).
The only challenge is staying still, but pillows will be provided to help limit movement.
If you want, someone can stay with you in the CT room during the scan.

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About radiation

A CT scan uses a small amount of X-ray radiation. For a single scan as part of getting your diagnosis, the risk is very low — and follow-up checks for Crohn’s are usually done with ultrasound or endoscopy, which use no radiation at all. Doctors only order a CT when the information it provides can’t be obtained another way, and modern scanners use the lowest dose that still gives useful images.

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Video Capsule Endoscopy (“Pillcam”)

A tiny camera in a swallowable capsule

With a capsule endoscopy, gastroenterologists examine the small intestines — which can’t be fully examined during a gastroscopy or colonoscopy. This safe, painless procedure is typically used in older children and teens, who can usually swallow the capsule (about the size of a large jellybean or vitamin). If swallowing the capsule is difficult, gastroenterologists can insert it during a gastroscopy.

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What happens after you swallow the capsule?

The capsule contains a camera that takes pictures as it moves through your small intestines. A device you wear around your waist records the pictures. The capsule will pass naturally with your stool within 1–3 days. Don’t worry — you usually won’t need to collect it.

📅 The day before

You’ll likely need to follow a clear liquid diet and drink a special bowel prep drink to clear out all the stool from your small intestines.

📅 The day of the procedure

You’ll wear a small recorder around your waist (like a fanny pack or bum bag) that records the pictures from the capsule.
After swallowing the capsule with water, you can resume most regular activities — but no sport or strenuous activity while wearing the recorder, since impact or sweat can affect it.
After a couple of hours, you can eat a light meal again.
About 8 hours later, you can usually remove the recorder, and your physician can start reviewing the pictures.

🧘 After the procedure

You’ll be able to resume your daily activities immediately.

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CT Enterography

A painless scan of the small and large intestines and stomach

A CT enterography is a painless procedure to examine the small and large intestines and the stomach.

📅 The day of the procedure

Do not eat or drink a few hours before the procedure.
You may usually take any regular medication; check with your medical team.
You will need to drink a special liquid contrast agent a few hours before the procedure within a certain time frame.
An IV will be set up to administer another contrast agent when scanning begins.
For the procedure itself, you’ll lie comfortably on a table in the CT room.
You’ll need to stay still during the scan; additional pillows and a call button for assistance will be in your hands.
Communication with staff is possible via an intercom system throughout the procedure.
During the scan, staff will administer the second contrast agent through the IV. It might feel a little warm but should not be painful.
A CT enterography takes about 30 minutes.

🧘 After the procedure

Once finished, the IV will be removed, and you may go home or return to your hospital room.
Drink a lot after the procedure to help flush out the contrast agent from your system.

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MR Enterography

A painless scan using magnetic fields (no radiation)

MR enterography is another painless procedure to examine the small and large intestines and the stomach.

📅 The day of the procedure

You’ll have to refrain from eating or drinking a few hours before the procedure.
An IV will be set up to administer a contrast agent later during the scan.
You will need to drink a liquid contrast agent within a certain time frame. This helps create clear images of the stomach and intestines.
You’ll then lie on a table that moves into the MRI machine (donut-like shaped structure).
Staying still is important for good-quality images, and pillows will be provided for comfort.
The MRI machine can be noisy — earplugs are available to help reduce the noise.
You’ll hold a call button for assistance if needed, and you can communicate with staff through an intercom system.
During the procedure, the second contrast agent will be administered through the IV. It might feel warm in the arm but should not be painful.
The procedure usually takes 45 minutes to 1 hour.

🧘 After the procedure

The IV will be removed, and you may go home or return to your hospital room.
Drink a lot after the procedure to help flush out the contrast agent.

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Ultrasound

Using sound waves to see inside your body

An ultrasound is an exam that creates images of your organs, tissues, and other structures inside your body by sending sound waves into it.

📋 For the exam

You don’t need any specific preparation, but you might have to fast for a few hours before the exam.
Remove your clothes from the area that will be examined.
The technician will apply gel to the area to reduce air between your body and the ultrasound device (the “transducer”) for clearer images.
During the exam, the technician moves the transducer around, sending sound waves into your body.
The transducer also collects the echoes, which are instantly displayed as images on a screen.

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Upper GI Series (Barium Swallow)

An X-ray exam of your upper gastrointestinal tract

Upper GI series is an imaging technique used to evaluate the upper gastrointestinal tract, including the esophagus, stomach, and the first part of the small intestines. It is less commonly used today, since MR enterography and ultrasound usually give better information with less radiation.

📅 The day before

Do not eat or drink after bedtime the night before the procedure.

📅 The day of the procedure

You’ll wear a hospital gown and might need to stand or lie on an X-ray table.
You will swallow a fluid called barium or another contrast agent, which coats the inside of your organs. This makes them show up white on an X-ray.
The radiologist will take X-ray pictures, or series of X-ray pictures, to observe the contrast agent/barium moving through your upper gastrointestinal tract.
During the procedure you’ll have to change into different positions.
The procedure usually takes about 30 minutes.

🧘 After the procedure

You can resume your regular activities.
Drink a lot of fluids to help flush out any remaining barium/contrast agent.

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Lower GI Series (Barium Enema)

An X-ray exam of your large intestines and rectum

A lower GI series, or barium enema, evaluates the large intestines, especially the left side (colon and rectum). Like the upper GI series, it is less commonly used today, since MR enterography and ultrasound usually give better information with less radiation.

📅 The day before

You’ll follow a clear liquid diet and take laxatives or medications to clean out your bowels.
Avoid eating or drinking after bedtime the night before the procedure.

📅 The day of the procedure

After changing into a hospital gown, you’ll lie on an X-ray table.
A fluid called barium or another contrast agent will be inserted into your rectum through a small tube to coat your intestines.
The radiologist will take pictures or series of X-ray pictures as the barium/contrast agent moves through your large intestines.
Expect to change positions during the procedure.

🧘 After the procedure

You can resume your regular activities.
Some of the barium/contrast agent will flow out of your body immediately after the procedure; the rest will pass in your stool later.
Drink a lot of fluids to help flush out any remaining barium/contrast agent.

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Gastroscopy

A camera exam of your upper GI tract, while you’re asleep

Gastroscopy — also called OGD or EGD — is a procedure that lets gastroenterologists examine the inside of your upper gastrointestinal tract: the esophagus, stomach, and first part of the small intestines (the duodenum).

📅 The day before

The only preparation needed is to avoid food or drinks, typically starting the night before the procedure.

📅 The day of the procedure

Before the procedure, you’ll meet with an anesthesiologist who will put you to sleep during the gastroscopy.
To do this, a needle (IV) will be inserted into one of your arms to give the anesthetics.
Once asleep, the gastroenterologist will insert a long, bendable tube with a light and a camera through your throat, down the esophagus, and into your stomach and duodenum.
As the tube moves through, real-time images will appear on screen allowing the physician to see if and where there is any inflammation.
The physician may also take tissue samples (“biopsies”) for further examination in a laboratory.
A gastroscopy usually takes about 20 minutes.

🧘 After the procedure

When you wake up, take it easy for the rest of the day and allow your body to recover. Normal activities can resume the next day.
You won’t be able to drive home — the anesthesia stays in your system for a while — so arrange for someone to pick you up.
You might also feel a bit sore in the throat or bloated for a few hours, but these symptoms will go away soon.

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Colonoscopy

A camera exam of your large intestines, while you’re asleep

A colonoscopy is similar to a gastroscopy, but examines the large intestines and the last part of your small intestines (terminal ileum).

📅 Days before the procedure

To examine the inside of your colon, it must be completely empty.
Your medical team will likely ask you to stop eating certain hard-to-digest foods like raw or dried fruits, foods with seeds (e.g., whole grain bread, tomatoes, cucumber).
The day before the procedure, you may also need to stop drinking milk or eating dairy products.
That same day, you’ll begin the bowel washout, which involves drinking a special bowel prep solution starting in the afternoon. This will mean a lot of trips to the bathroom over a few hours — it’s the least fun part of the procedure, but it makes the colonoscopy possible.
You can mix the bowel prep with certain drinks — ask your provider which ones you can mix.
Once you start the washout, plan to stay home, as you’ll be using the restrooms a lot for several hours.
Your large intestines should be empty once your stool looks like clear chamomile tea or apple juice without any solid pieces.

📅 The day of the procedure

The doctor inserts a tube into the anus and guides it through the rectum and colon up to the terminal ileum.
After finishing the bowel prep, you must fast and avoid eating or drinking.
If you take medication, discuss with your medical team when and if you should take it on the day of your procedure.
Before your colonoscopy starts, you’ll meet with an anesthesiologist who will insert a needle into your arm to inject anesthesia.
Once you are asleep, the gastroenterologist will begin the colonoscopy, during which tissue samples (“biopsies”) will be taken, or polyps removed, for further examination in a laboratory.
You won’t feel any of this, as you’ll be fully sedated during the procedure.

🧘 After the procedure

If you are an outpatient, you’re allowed to go home, but someone must pick you up — you won’t be allowed to drive since the sedative will still be in your system.
Take it easy for the rest of the day, avoid driving or operating machinery, and eat light meals.
You might feel a little bloated or gassy and need to pass gas, but these symptoms will go away within a few hours.

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TeenHealthInsight is a health education website — not a substitute for medical advice. Any questions or worries about an upcoming procedure should be brought to your doctor or gastroenterologist. Trust your gut (literally) — if something feels off, reach out to your medical team.