The short answer
A flexible sigmoidoscopy uses a thin, lighted tube to examine the rectum and the lower part of the colon. The prep is lighter than for a colonoscopy and most people don't need sedation, but it only sees part of the colon, so it's often paired with a stool test.
Sigmoidoscopy examines only the rectum and lower (sigmoid) colon, not the whole colon.
The prep is less involved than for a colonoscopy, and most people don't need sedation.
Abnormal growths in the area examined can be removed or biopsied during the test.
It is usually repeated every 5 to 10 years, sometimes paired with a stool test like FIT.
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The full explanation.
The simple version
A flexible sigmoidoscopy uses a sigmoidoscope — a thin, flexible, lighted tube with a camera — to look at the rectum and the lower part of the colon, called the sigmoid colon. The tube is gently passed through the anus into the rectum and lower colon.
Think of it as a shorter version of a colonoscopy. It examines less of the colon, which means a lighter prep and, for most people, no sedation. The trade-off is that it does not see the upper parts of the colon.
Sigmoidoscopy checks the lower colon and rectum with less prep than a colonoscopy — but it doesn't see the whole colon.
What it examines
The colon is a long tube, and cancers and polyps can form anywhere along it. A sigmoidoscopy reaches the rectum and the sigmoid colon — the lower, S-shaped section — but not the parts higher up.
That is the key limitation to understand. If a problem is developing in the upper colon, a sigmoidoscopy alone will not find it. This is why it is sometimes combined with a stool test that can catch signs of bleeding from anywhere in the colon.
The prep and the procedure
The lower colon still needs to be cleared of stool so the doctor can see clearly, but the prep is less extensive than for a colonoscopy. Your care team will give you specific instructions.
During the test:
- You usually stay awake — most people do not need sedation
- A little air is used to open the area so the doctor can see
- The exam is generally quick
If the doctor finds an abnormal growth in the area, it can often be removed or biopsied — a small sample taken and checked under a microscope.
Lighter prep and no sedation make sigmoidoscopy easier, but it covers less ground.
Who might consider it
Sigmoidoscopy is one of several approved colorectal screening options for people at average risk. It may appeal to someone who wants to avoid the fuller prep and sedation that a colonoscopy requires, but who still wants a direct look at part of the colon rather than only an at-home stool test.
Like every option, it involves trade-offs. Because it examines only the lower colon, it offers less complete coverage than a colonoscopy. Pairing it with a stool test helps close that gap. Your care team can help you decide whether this balance fits your preferences and your level of risk.
Sigmoidoscopy is a middle-ground option — more direct than a stool test, less complete than a colonoscopy.
How often, and pairing with a stool test
For people at average risk, experts generally recommend a screening sigmoidoscopy every 5 to 10 years. Because it does not see the whole colon, it is sometimes paired with a stool test, such as FIT, done every few years. The stool test helps catch signs of problems higher up that the scope cannot reach.
Sigmoidoscopy is often paired with a stool test to help cover the parts of the colon it can't see.
When a colonoscopy comes next
If the sigmoidoscopy finds an abnormality — such as a polyp — your doctor will often recommend a full colonoscopy. That test examines the entire colon, both to check the areas the sigmoidoscopy could not reach and to remove any growths found along the way.
In other words, a sigmoidoscopy can be a first step that sometimes leads to a colonoscopy. Finding something on a sigmoidoscopy does not mean you have cancer — most growths are polyps that can be examined and, if needed, removed during the follow-up colonoscopy. What matters is getting that recommended next step so the rest of the colon is checked too.
A finding on sigmoidoscopy usually leads to a colonoscopy — an important follow-up, not a diagnosis.
Availability and access
In the United States, sigmoidoscopy is used less often than colonoscopy and is not available everywhere. Colorectal cancer screening is a preventive service that many insurance plans and Medicare are required to help cover, but the specific tests offered vary by location and provider.
If this option interests you, ask your care team whether it is available near you and whether it suits your risk level.
Sigmoidoscopy is a valid but less common option — ask whether it's available and right for you.
Words to know
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Common questions
▸How is sigmoidoscopy different from a colonoscopy?
A colonoscopy examines the entire colon and rectum, while a sigmoidoscopy examines only the rectum and the lower (sigmoid) part of the colon. Because it looks at less of the colon, the prep is lighter and sedation usually isn't needed — but it can miss problems higher up.
▸Do I need to do a bowel prep?
Yes, but it is less extensive than the prep for a colonoscopy. The lower colon must be cleared of stool so the doctor can see clearly. Your care team will give you specific instructions on how to prepare.
▸Will I be sedated?
Usually not. Most people do not need sedation for a sigmoidoscopy. You may feel some pressure, cramping, or bloating as air is gently used to open the area, but this typically passes quickly after the test.
▸How often do I need it?
Experts generally recommend a screening sigmoidoscopy every 5 to 10 years for people at average risk. It is sometimes paired with a stool test, such as FIT, done every few years to help check for problems higher in the colon.
▸What if the doctor finds something?
Abnormal growths in the rectum or sigmoid colon can sometimes be removed or biopsied during the exam. If an abnormality is found, your doctor will often recommend a full colonoscopy to examine the rest of the colon that the sigmoidoscopy could not reach.
▸Is sigmoidoscopy widely available?
In the United States it is used less often than colonoscopy and is not available everywhere. If you are interested in this option, your care team can tell you whether it's offered in your area and whether it fits your situation.
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