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. NIDDK says it often takes less bowel prep, and you typically do not need 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.

The lower colon still needs to be cleared of stool so the doctor can see clearly. But NIDDK says it often needs less prep than 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.

USPSTF lists sigmoidoscopy as one of several recommended colorectal screening options. It may suit someone who wants less prep and no sedation. 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. 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.

USPSTF recommends a screening sigmoidoscopy every 5 years, or every 10 years together with a FIT stool test every year. It does not see the whole colon, so it is paired with a stool test in the second schedule. Ask your care team which schedule fits you.

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 cancer has been found. NIDDK says polyps are common and harmless in most cases, but most colon cancers begin as a polyp. That is why they are removed and checked. 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. Insurance plans and Medicare sometimes change whether and how often they pay for screening tests. Check with your plan. The tests offered also 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, dizzy or close to passing out. NIDDK says perforation (a tear in the colon) and bleeding are the most common complications, but both are rare. Do not drive yourself.
• Call your care team right away, day or night, if you have a fever, vomiting, severe pain or bloating in your belly, bloody bowel movements that do not get better, or bleeding from the anus that does not stop. NIDDK says to seek care right away for these. Use 100.4°F (38°C) as your fever line.
• Call your care team the same day if blood reappears after it had stopped. NIDDK says delayed bleeding can happen several days after the test.
• Call your care team within a day or two if the cramping and bloating have not eased off.

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