A sigmoidoscopy is a procedure that lets a doctor examine the lower third of your large intestine, specifically the rectum and sigmoid colon, using a thin, flexible tube with a tiny camera on the end. The whole thing typically takes 10 to 20 minutes, and most people go home the same day without needing sedation. It’s one of several tools used to screen for colorectal cancer, investigate unexplained symptoms like rectal bleeding, and diagnose conditions affecting the lower bowel.
What the Procedure Examines
The sigmoid colon is the S-shaped section of your large intestine that sits just above the rectum. It makes up roughly one-third of the total colon. During a sigmoidoscopy, the scope travels through the anus, past the rectum, and into the sigmoid colon. As it moves, a small video camera at the tip sends a live image to a monitor so the doctor can inspect the intestinal lining in detail.
This is a key distinction from a colonoscopy, which examines the entire colon. A sigmoidoscopy only looks at the lower portion. If something abnormal is found, or if the doctor needs to see higher up, a full colonoscopy may be recommended as a follow-up.
Why It’s Done
Sigmoidoscopy serves two broad purposes: screening and diagnosis. As a screening tool for colorectal cancer, the U.S. Preventive Services Task Force lists flexible sigmoidoscopy every five years as one of the accepted options for adults in the recommended screening age range. Because it doesn’t require the full bowel prep or sedation of a colonoscopy, some people find it a more accessible first step.
Diagnostically, a doctor might order one if you’re experiencing rectal bleeding, changes in bowel habits, chronic diarrhea, or unexplained abdominal pain localized to the lower left side. During the procedure, the doctor can take small tissue samples (biopsies) or remove polyps for laboratory analysis, which helps confirm or rule out conditions like inflammatory bowel disease or early-stage cancer.
Flexible vs. Rigid Sigmoidoscopy
Almost all sigmoidoscopies today use a flexible scope, but a rigid version still exists. The rigid sigmoidoscope is a shorter, straight tube that can’t navigate the colon’s curves as easily. In a direct comparison study, over 33% of patients declared normal by rigid sigmoidoscopy actually had significant findings, including polyps and malignant lesions, when re-examined with a flexible scope. The flexible version is more comfortable, reaches further, and makes it easier to take biopsies or remove polyps. If your doctor orders a sigmoidoscopy, it will almost certainly be the flexible type.
How to Prepare
Preparation for a sigmoidoscopy is simpler than for a colonoscopy, but there are still steps to follow. Starting about a week beforehand, you’ll want to stop eating foods that are hard to clear from the colon, like corn, popcorn, seeds, and nuts. Iron supplements should also be stopped, since they can discolor the colon lining and make it harder to spot abnormalities.
Three days before the procedure, you may be asked to stop taking vitamin E, fish oil, mineral oil, and flaxseed oil, all of which can increase bleeding risk. You’ll also need to pick up two Fleet enemas from a pharmacy. The night before, you’ll stop eating solid food after midnight. On the morning of the procedure, you can take sips of clear liquids and your regular medications up to four hours before your appointment. The two enemas are typically self-administered at home about an hour before you leave for the clinic. The goal is simply to clear out the lower colon so the camera has an unobstructed view.
What Happens During the Procedure
You’ll lie on your left side on an exam table, usually with your knees drawn toward your chest. The doctor inserts the lubricated sigmoidoscope through the anus and slowly advances it into the rectum and sigmoid colon. As it moves forward, the scope pumps a small amount of carbon dioxide gas into the intestine to inflate it, which gives the camera a clearer view of the lining.
Most people do not need sedation or anesthesia. The procedure isn’t painful, but you’ll likely feel some pressure, cramping, or the urge to have a bowel movement as the scope advances. The gas can cause a bloated feeling, though it passes relatively quickly after the exam. You may be asked to shift positions on the table a few times so the doctor can angle the scope for a better look. If a biopsy or polyp removal is needed, small instruments are passed through the scope to collect tissue. You typically won’t feel this part. The whole process, including any biopsies, usually wraps up in 15 to 20 minutes.
Risks and Safety
Sigmoidoscopy is one of the lowest-risk endoscopic procedures. A large meta-analysis looking at screening populations found a bleeding rate of about 8 per 100,000 people screened with sigmoidoscopy. For comparison, colonoscopy following a positive stool test had a bleeding rate of 229 per 100,000. Perforation, the most serious potential complication, was so rare in sigmoidoscopy screening data that it couldn’t be meaningfully estimated in the analysis. For colonoscopy, perforation occurred in roughly 53 to 88 per 100,000 screenings depending on the context.
In practical terms, this means complications from sigmoidoscopy are uncommon. The combination of a shorter scope, less manipulation, and typically no sedation all contribute to the favorable safety profile.
Recovery and Getting Results
Because most sigmoidoscopies are done without sedation, you can generally drive yourself home and return to normal activities right away. Bloating and mild gas are common for a few hours afterward as the carbon dioxide works its way out, but this resolves on its own. You can eat and drink normally after the procedure.
If the doctor took biopsies or removed polyps, those tissue samples are sent to a laboratory for examination under a microscope. Results typically come back in one to two weeks, though the timing can vary depending on the lab and whether specialized testing is needed. If everything looked normal during the visual exam and no samples were taken, you’ll often get a preliminary result before you leave the office. If polyps or other concerning findings are discovered, your doctor will discuss next steps, which may include scheduling a full colonoscopy to examine the rest of the colon.