A small bowel series is an imaging test that uses X-rays and a chalky liquid called barium to create detailed pictures of your small intestine. You drink the barium, which coats the lining of your digestive tract and makes it visible on X-ray images. A radiologist then takes a sequence of images as the barium moves through your small intestine, looking for abnormalities like narrowing, inflammation, blockages, or tumors.
The test is also called a “small bowel follow-through” because the radiologist literally follows the barium’s progress through roughly 20 feet of small intestine using a type of real-time X-ray called fluoroscopy.
Why Doctors Order This Test
A small bowel series is typically ordered when your doctor suspects a problem in the small intestine that wouldn’t show up on a standard X-ray or blood test. Common reasons include unexplained abdominal pain, chronic diarrhea, unexpected weight loss, or signs of bleeding in the digestive tract. The test can reveal a range of conditions: inflammation of the intestinal lining (as seen in Crohn’s disease), strictures where the intestine has narrowed, small pouches called diverticula, tumors, ulcers, and malabsorption problems where the intestine isn’t properly absorbing nutrients.
It’s also used to evaluate intestinal obstructions, gastroparesis (where the stomach empties too slowly), and gastroesophageal reflux disease. If you’ve had surgery on your small intestine, a small bowel series can help check how things are healing or whether new problems have developed.
How to Prepare
You’ll need an empty stomach for the test. For adults and children over 2, that means no food or drink for at least six hours beforehand. For younger children, the fasting window is shorter: four hours for ages 7 to 24 months, and three hours for infants under 6 months. Your doctor may also ask you to stop certain medications temporarily, so mention everything you take when scheduling the appointment.
If you’ve ever had an allergic reaction to barium or any radiographic contrast material, let your care team know ahead of time. Additional precautions may be needed.
What Happens During the Test
The test begins with you drinking a thick, white barium solution. Most people describe the taste as chalky, though some facilities flavor it to make it more tolerable. Once you’ve finished drinking, the radiologist positions you on an X-ray table and takes the first set of images.
From there, it becomes a waiting game. Barium moves through the small intestine at its own pace, and the radiologist takes new images at regular intervals, typically every 15 to 30 minutes. Between images, you’ll wait in a nearby area. Occasionally, the radiologist will use fluoroscopy to watch the barium move in real time, pressing gently on your abdomen to spread the barium and get clearer views of specific areas.
The entire process usually takes one to four hours, depending on how quickly the barium travels through your system. Some people move it through in under an hour; for others, it takes longer. You can’t speed this up, so plan for a longer appointment than you might expect.
Radiation Exposure
A small bowel series does involve radiation, but the dose is relatively modest. Studies measuring radiation exposure during this test found a typical effective dose of about 1.8 to 2.2 millisieverts (mSv), which includes both the fluoroscopy time and the individual X-ray images taken. For context, a CT scan of the abdomen delivers roughly 3.5 mSv, so a small bowel series exposes you to about half to two-thirds the radiation of a CT. A single chest X-ray delivers around 0.02 mSv, making a small bowel series roughly 100 times that amount.
This is considered a low-to-moderate dose. For a one-time diagnostic test, the benefit of identifying a problem in your small intestine generally outweighs the radiation risk. For patients who need repeated imaging over time, such as those with Crohn’s disease, doctors may consider alternatives like MRI-based imaging to reduce cumulative exposure.
After the Test: Side Effects
The most common side effect is constipation. Barium can harden in the intestines if it isn’t flushed out, so you’ll be encouraged to drink plenty of fluids in the hours and days after the test. Some people also experience mild cramping, bloating, or diarrhea as the barium passes through.
Your stools will look white or light-colored for a day or two. This is normal and simply means the barium is leaving your body. If constipation becomes severe or you develop significant abdominal pain, nausea, or vomiting after the test, contact your doctor. These symptoms are uncommon but can indicate the barium isn’t moving through properly.
The test is not safe for everyone. People with a known or suspected bowel obstruction, perforation, or severe bowel inflammation (such as toxic megacolon) should not drink barium, as it can worsen these conditions or leak into the abdominal cavity.
Small Bowel Series vs. CT and MRI
The traditional small bowel series has been a diagnostic workhorse for decades, but it’s increasingly being complemented or replaced by CT enterography and MR enterography for certain conditions. CT enterography pairs a CT scanner with a special oral contrast to produce cross-sectional images of the bowel wall and surrounding tissues. It’s faster, often completed in minutes rather than hours, and can detect problems both inside and outside the intestinal wall, like abscesses or fistulas.
MR enterography offers similar detail without radiation, making it particularly useful for younger patients or those who need repeated imaging over time. For Crohn’s disease monitoring, many gastroenterologists now prefer MR enterography for exactly this reason.
That said, a small bowel series still has practical advantages. It’s widely available, less expensive, and particularly good at showing how the intestine moves and functions in real time. Your doctor will choose the test that best fits your specific situation, the available technology, and what they’re looking for.