A “lower GI” refers to the lower gastrointestinal tract, the final stretch of your digestive system. It also commonly refers to a lower GI series, a diagnostic imaging procedure that uses X-rays and a contrast liquid called barium to examine that part of your body. If your doctor mentioned a “lower GI,” they’re most likely talking about the procedure. Here’s what both terms mean and what to expect.
The Lower GI Tract
Your lower gastrointestinal tract is everything from the end of the small intestine down. It consists of the large intestine and the anus. The large intestine itself contains several distinct parts: the cecum (a small pouch where the small intestine connects), the appendix, the colon, and the rectum.
The colon is the longest section, and it’s divided into four parts that form a rough frame around your abdomen: the ascending colon (running up the right side), the transverse colon (crossing left), the descending colon (running down the left side), and the sigmoid colon (an S-shaped curve that connects to the rectum). The rectum leads to the anus, a roughly one-inch opening where stool leaves the body. Together, these organs absorb water from digested food, form stool, and move it toward elimination.
What a Lower GI Series Is
A lower GI series, also called a barium enema, is an X-ray procedure designed to give doctors a detailed look at your large intestine. On a standard X-ray, soft tissue like the intestinal wall doesn’t show up clearly. Barium, a chalky white liquid, coats the inside of your colon and makes those structures visible on the images.
There are two types. A single-contrast lower GI series uses barium alone. A double-contrast (or air-contrast) version uses both barium and air, which inflates the colon and provides a clearer, more detailed picture. Your doctor will choose the type based on what they’re looking for.
Why Doctors Order This Test
A lower GI series helps identify structural problems and abnormalities in the large intestine. It can reveal polyps, tumors, areas of inflammation, pouches in the colon wall (diverticulosis), narrowing or blockages, and other changes in the shape or lining of the bowel. Doctors may order it when someone has persistent symptoms like unexplained changes in bowel habits, chronic abdominal pain, rectal bleeding, or unexplained weight loss.
In many cases today, colonoscopy or CT-based imaging has replaced the traditional barium enema because those methods can provide even more detail or allow tissue samples to be taken at the same time. But a lower GI series remains a useful option, particularly for people who can’t undergo colonoscopy or when a broad view of the colon’s shape is needed.
What Happens During the Procedure
A lower GI series takes about 30 to 60 minutes and is performed by a radiologist or radiology technician, typically at a hospital or outpatient imaging center. You won’t receive sedation or anesthesia, so you’ll be awake and able to talk with the team throughout.
After changing into a hospital gown, you’ll lie on your side on an exam table. The technician will gently insert a lubricated, flexible tube into your rectum. Liquid barium flows through the tube and fills your large intestine. A small balloon at the tip of the tube inflates to prevent leakage. If you’re having a double-contrast study, air is also pumped in through the same tube to expand the colon.
As barium (and possibly air) fills your bowel, you’ll likely feel uncomfortably full or feel pressure, similar to the urge to have a bowel movement. This is normal and temporary. You’ll be asked to hold still in various positions, and sometimes hold your breath briefly, so the team can capture clear X-ray images. They may also record a type of real-time X-ray video called fluoroscopy to watch the barium move through your colon.
After the Test
Once imaging is finished, the balloon is deflated and most of the barium drains out through the tube. You’ll then be given access to a toilet or bedpan to expel whatever barium remains. In some cases, a follow-up enema may be given to help flush out the rest.
Expect your stool to look white or light-colored for a day or two afterward as remaining barium passes through. Drinking extra fluids helps move it along. Some people experience mild bloating or cramping for a few hours, but most can return to normal activities right away. There’s no recovery period needed since no sedation is involved.
Risks and Safety
A lower GI series is considered a low-risk procedure. The most serious potential complication is perforation, where the pressure of barium or air creates a small tear in the bowel wall. This is rare. For comparison, bowel perforation during diagnostic colonoscopy occurs in fewer than 1 in 2,000 cases, and a barium enema carries a similarly low risk profile. Certain conditions increase vulnerability, including severe diverticular disease, active inflammatory bowel disease, and significant scarring or adhesions in the colon.
The procedure also involves a small dose of radiation from the X-rays. The amount is modest and generally considered safe for occasional diagnostic use, though it’s a reason doctors avoid ordering the test unless it’s clearly needed.
Lower GI Series vs. Colonoscopy
Both tests examine the large intestine, but they work differently. A lower GI series produces X-ray images of the colon’s outline. A colonoscopy uses a flexible camera inserted through the rectum to view the colon’s interior directly, and it allows the doctor to remove polyps or take tissue samples during the same session.
Colonoscopy is generally preferred for cancer screening and for investigating symptoms where a biopsy might be needed. A lower GI series may be recommended instead when colonoscopy isn’t feasible, for instance if a person has certain medical conditions that make sedation risky, or if the colonoscope can’t pass through a narrowed section of bowel. Both procedures require bowel preparation beforehand to clear the colon for a clean view.