Flexible Sigmoidoscopy: Screening the Lower Colon

A flexible sigmoidoscopy uses a sigmoidoscope — a thin, flexible, lighted tube with a camera. It looks at the rectum and the lower part of the colon, called the sigmoid colon. The tube is passed gently 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. That 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.

The colon is a long tube. Cancers and polyps can form anywhere along it. A sigmoidoscopy reaches the rectum and the sigmoid colon, the lower, S-shaped section. It does not reach the parts higher up.

That is the key limit to understand. If a problem is growing in the upper colon, a sigmoidoscopy alone will not find it. So it is sometimes paired with a stool test. A stool test can catch signs of bleeding from anywhere in the colon.

The lower colon still needs to be cleared of stool so the doctor can see clearly. But the prep is lighter 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

Does the doctor find an odd 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.

Sigmoidoscopy is one of several approved colorectal screening options for people at average risk. It may suit someone who wants to avoid the fuller prep and the sedation a colonoscopy requires. It may also suit someone who still wants a direct look at part of the colon, not just an at-home stool test.

Like every option, it involves trade-offs. It examines only the lower colon, so it covers less ground 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.

For people at average risk, experts generally recommend a screening sigmoidoscopy every 5 to 10 years. It does not see the whole colon, so it is sometimes paired with a stool test, such as FIT, done every few years. The stool test helps catch signs of trouble 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.

Say the sigmoidoscopy finds something abnormal, such as a polyp. Your doctor will often then recommend a full colonoscopy. That test examines the entire colon. It checks the areas the sigmoidoscopy could not reach, and it removes any growths found along the way.

So 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. They can be examined and, if needed, removed during the follow-up colonoscopy. What matters is getting that 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.

In the United States, sigmoidoscopy is used less often than colonoscopy, and it 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.

Does this option interest 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.

Cramping, bloating and a little blood from the anus for a day or so are expected after the scope. A few problems are not, and they are worth acting on quickly.

• Call 911 or go to an emergency department if your belly turns severely painful or hard in the hours or days after the test, or blood pours from the anus rather than trickling, or you feel faint, weak or close to passing out. These point to a tear in the bowel wall or heavy bleeding from a biopsy site. Both are rare. Both need care straight away.
• Call your care team the same day if you run a temperature of 100.4°F (38°C) or higher, or bloody bowel movements keep coming instead of settling down.
• Call your care team within a day or two if the cramping and bloating have not eased off, or blood reappears after it had already stopped.

Sources for this section: NIDDK — Flexible Sigmoidoscopy, NIDDK — Colonoscopy, American Cancer Society — Colorectal Cancer Screening Tests.