A sigmoidoscopy is a test a doctor uses to examine the lower portion of the colon. This procedure can help detect conditions such as colorectal cancer.

A sigmoidoscopy involves using a thin instrument shaped like a tube, known as a sigmoidoscope. This instrument contains a camera and a light to examine the inside of the colon.

Read on to explore how a sigmoidoscopy works, the preparation, procedure, and what to expect. We also discuss how to interpret the biopsy results, potential risks of the procedure, and frequently asked questions.

A diagram of the intestines with a sigmoidoscope checking for any abnormalitiesShare on Pinterest
Illustration by Jason Hoffman

A sigmoidoscopy examines the lower area of the large intestine or colon. Doctors refer to the lower part of the colon as the sigmoid colon.

A doctor inserts a sigmoidoscope through the anus and rectum during a sigmoidoscopy. They gently guide the sigmoidoscope through the sigmoid colon to look for abnormalities, such as polyps or growths.

If a doctor observes any irregularities during a sigmoidoscopy, they may order a colonoscopy, a more comprehensive examination that can provide further information on an individual’s gastrointestinal health.

Although this test is similar to a sigmoidoscopy, it examines a different body part. A sigmoidoscopy examines only the lower part of the colon, whereas a colonoscopy examines the entire colon.

A sigmoidoscopy detects abnormal growth in the lower colon. Individuals may require a sigmoidoscopy if they experience:

Sigmoidoscopy can detect unusual growths, such as polyps. Colorectal polyps are pieces of extra tissue that grow inside the colon. In most cases, polyps are not an immediate cause for concern.

However, in certain instances, they may be cancerous or become cancerous at a later stage. A doctor may choose to run further tests after a sigmoidoscopy if polyps are present.

A sigmoidoscopy is a useful tool for polyps and colorectal cancer screening. Detecting polyps and other growths can accelerate treatment. Treating conditions such as colorectal cancer maximizes the chance of a full recovery.

Learn more about polyps here.

Certain individuals may be at a higher risk for colon cancers. These may include individuals with:

Individuals preparing for a sigmoidoscopy should contact their doctor for preparation instructions. The following general guidance may or may not apply to each case.

Dietary changes

In most cases, preparing for a sigmoidoscopy will require a special diet. Doctors may recommend a liquid diet for 24 hours before the procedure.

A liquid diet will minimize the amount of stool inside the colon. This will make it easier for the test professional to visualize any potential problems.

Foods that are appropriate for this stage may include:

A person can speak with a doctor to learn more about dietary preparation for a sigmoidoscopy.

Emptying the colon

In addition to dietary changes, emptying the colon is an important part of sigmoidoscopy preparation. A doctor may suggest laxatives or an enema before the procedure.

Emptying the colon makes it easier for a medical professional to conduct a sigmoidoscopy. Individuals in this preparation stage should stay near a bathroom facility.

Medication adjustments

Some people may need to avoid taking medications on the day of the procedure. People may have to avoid some medications for up to 2 weeks before a sigmoidoscopy.

However, it is generally safe to continue taking medications for the following conditions:

A person can consult doctors to discuss what medications or supplements they take regularly. Medical professionals will review this information and advise people on any drugs they should avoid before a sigmoidoscopy.

During a sigmoidoscopy, a person will lie on their left side and draw their knees into their chest. The doctor then performs a digital rectal exam. This helps them prepare the anal opening to receive the sigmoidoscope.

The doctor will insert the sigmoidoscope into the anus and gently guide the instrument through the colon. The scope sends images to a video monitor.

The doctor reviews these images to determine whether further action is needed. If any abnormalities are present, they may conduct a biopsy.

A biopsy involves the removal of small pieces of tissue from the colon. After a biopsy, the doctor will send tissue samples to a laboratory for further analysis. They may also choose to remove polyps during the sigmoidoscopy procedure itself.

Doctors can complete sigmoidoscopy with or without sedation. If they recommend sedation, a driver must be present on the day of the procedure.

Individuals who have a sigmoidoscopy may experience mild symptoms after this test. For example, soreness and mild stomach discomfort may occur a day after the procedure.

Anyone experiencing more severe symptoms after a sigmoidoscopy should consult a medical professional, such as severe bleeding or fever, which may indicate an adverse reaction.

If a person has a biopsy during a sigmoidoscopy, they should receive a pathology report. This report provides detailed information about the tissue sample and relevant treatment recommendations.

Individuals who receive a pathology report after their sigmoidoscopy should consult a doctor for any questions about interpreting their results.

Type of polyp

If a doctor takes a biopsy of a colon polyp, the pathology report will explain what type it is.

The most common type of colon polyp is called tubular adenoma. When doctors detect these in their early stages, they can treat these polyps by removing them during a colonoscopy.

A villous adenoma is less common than a tubular adenoma, but this polyp has a higher risk of developing cancer. Doctors may remove it during a colonoscopy, or a person may need surgery. A pseudopolyp is also fairly common during a sigmoidoscopy.

Read more about the types of colon polyps.

Polyp removal

Doctors may perform an endoscopic mucosal resection (EMR), which refers to the removal of a polyp. The tissue removed will include a small area of the surface lining of the bowel. However, an EMR is not a routine procedure during a sigmoidoscopy.

Types of tumors

The most common type of colon tumor is called adenocarcinoma. The pathology report from a sigmoidoscopy does not typically include a tumor grade as it is a superficial biopsy.

If a person has cancer, they usually receive a tumor grade following an EMR or surgical removal of the mass.

Learn more about different types of tumors.

This procedure is less invasive than other tests, such as colonoscopies, so most individuals do not experience severe side effects.

The potential risks following a sigmoidoscopy include:

The doctor diagnoses and treats delayed bleeding with a colonoscopy or repeat sigmoidoscopy. They may also need to treat perforation with surgery.

Individuals should consult a doctor if these or any other unexplained symptoms occur.

The prospect of going through a sigmoidoscopy may feel overwhelming at first. The best way for people to prepare is to be well-informed about the procedure and discuss any concerns with a doctor.

Some common questions about sigmoidoscopy are below.

Is it painful?

A sigmoidoscopy may cause mild discomfort. The sensation of the scope passing through the colon may feel uncomfortable for a short period. But the healthcare professional performing this procedure will move the scope slowly and gently to avoid sharp pain.

Who performs a sigmoidoscopy?

In most cases, the person performing a sigmoidoscopy will specialize in the digestive system. This is usually a gastroenterologist, a surgeon, a nurse practitioner, or a physician assistant.

Are you awake during the procedure?

Individuals having a sigmoidoscopy will be awake for the procedure. The test takes about 20 minutes and does not cause pain.

Although anesthesia is unnecessary, people may request it, or the doctor may recommend it to help someone feel more comfortable.

Is it safe?

A sigmoidoscopy is a safe and routine procedure. People may experience mild side effects during and afterward but generally do not experience serious side effects.

A sigmoidoscopy is a standard test to examine the lower colon. This procedure uses a scope that relays images of the colon’s interior to a screen.

Medical professionals use sigmoidoscopy to identify any irregularities inside the colon. They may also take tissue samples of any growths for laboratory analysis.

This procedure is a quick and effective way to determine whether further tests are needed. Individuals seeking a sigmoidoscopy should consult with a medical professional to learn more.