A flex sig, short for flexible sigmoidoscopy, is a quick exam that lets a doctor look inside the lower part of your colon using a thin, flexible tube with a tiny camera on the end. The procedure typically takes about 15 to 20 minutes and usually doesn’t require sedation, which sets it apart from a full colonoscopy.
What Happens During the Procedure
During a flexible sigmoidoscopy, a doctor inserts a narrow, flexible tube called a sigmoidoscope into the rectum and guides it through the sigmoid colon, which is the S-shaped lower section of the large intestine. The camera on the tip sends images to a screen, giving the doctor a real-time view of the intestinal lining. If anything abnormal is spotted, such as a polyp or inflamed tissue, the doctor can take a small tissue sample (biopsy) during the same exam. Biopsies may add a few extra minutes to the procedure.
Most people stay awake and alert throughout. You’ll likely feel some pressure, cramping, or bloating as the scope moves through the colon and air is used to expand the area for better visibility. These sensations are usually mild and temporary.
How It Differs From a Colonoscopy
The two biggest differences between a flex sig and a colonoscopy are how far the scope travels and whether you need sedation. A colonoscopy examines the rectum and the entire large intestine, while a flexible sigmoidoscopy only looks at the rectum and the lower portion. Because a flex sig covers less territory, it’s shorter, simpler, and sedation is usually not required. A colonoscopy typically requires sedation to keep you comfortable while the scope navigates the full length of the colon.
The trade-off is coverage. A flex sig can detect problems in the lower colon, but it won’t catch polyps or other issues higher up. If polyps are found during a flex sig, your doctor will often recommend a full colonoscopy to check the rest of the colon.
Why Doctors Order a Flex Sig
There are two main reasons you might be scheduled for a flexible sigmoidoscopy: screening for colorectal cancer or investigating specific symptoms. As a screening tool, it can detect precancerous polyps in the lower colon before they develop into cancer. The U.S. Preventive Services Task Force includes it among the recommended options for colorectal cancer screening starting at age 45.
Doctors also use it to look for the cause of symptoms like rectal bleeding, chronic diarrhea, unexplained abdominal pain, or changes in bowel habits. It’s particularly useful when the suspected problem is in the lower colon or rectum, since it can provide a direct visual diagnosis without the prep and sedation required for a colonoscopy.
What Prep Looks Like
The preparation for a flex sig is lighter than what’s required for a colonoscopy. Because only the lower colon needs to be clear, the prep typically involves one or two enemas on the morning of the procedure rather than drinking a full bowel-prep solution the night before. Your doctor may also ask you to adjust your diet for a day or so beforehand, avoiding high-fiber foods or seeds that could obscure the view. Specific instructions vary by practice, so follow whatever your doctor’s office provides.
Recovery and Getting Results
Since sedation isn’t typically used, most people can drive themselves home and return to normal activities the same day. You may experience mild bloating or gas for a few hours afterward as the air introduced during the exam works its way out. This is normal and resolves on its own.
If no biopsies were taken, your doctor can often share preliminary results right after the procedure. When tissue samples are collected, lab results usually take a few days. Your doctor will let you know whether any follow-up is needed, which could range from a repeat screening in several years to a full colonoscopy if polyps or other concerns were found.
Risks Are Rare
Flexible sigmoidoscopy is considered very safe. The most serious potential complications, bowel perforation and significant bleeding, occur in a small fraction of cases. Studies on similar endoscopic procedures report perforation rates between roughly 0.05% and 0.11%, and bleeding rates that have dropped to well under 1% with modern techniques. For a flex sig specifically, the risk is on the lower end of these ranges because the scope travels a shorter distance and the procedure is less invasive overall. Most people experience nothing more than brief cramping or mild soreness.