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Female healthcare provider smiling and holding the hand of a female patient resting in a recovery bed after a sigmoidoscopy

What is a sigmoidoscopy?

A sigmoidoscopy is an endoscopy procedure that uses a thin tube with a tiny camera to view the inside of your rectum and lower colon—called the sigmoid colon. You may have this exam if you have anal, rectal or colon symptoms or to screen for colorectal cancer.

During a sigmoidoscopy, your provider can take images and collect small tissue samples to help diagnose your condition. It’s important to know that a sigmoidoscopy only lets your care team see about a third of your colon. Other procedures are needed to view the entire colon.

Types of sigmoidoscopy

Sigmoidoscopy is grouped into two types of procedures, depending on the tools used and how much of the lower digestive tract is viewed. In general, a flexible sigmoidoscopy views more of the digestive tract, comes with less discomfort and allows your care team more access to take tissue samples.

  • Flexible sigmoidoscopy

    With flexible sigmoidoscopy, your doctor uses a flexible tube or scope. This tube is longer than the scope used in rigid sigmoidoscopy, allowing your team to view more of the lower colon.

  • Proctoscopy (rigid sigmoidoscopy)

    A proctoscopy or rigid sigmoidoscopy is more commonly used to view the anus and rectum. The scope used in a proctoscopy is shorter and less flexible.

Sigmoidoscopy vs colonoscopy

Sigmoidoscopy and colonoscopy are both endoscopy procedures, which means they both use a scope (tube) with a camera to diagnose conditions in the digestive tract or look for signs of cancer during a colon cancer screening. The prep is also the same.

The biggest difference between the two procedures is how much of the colon your care team examines. Sigmoidoscopy views the last two feet, while colonoscopy views the entire colon.

Sigmoidoscopy

  • Uses a thin tube and a small camera
  • Requires prep to clean out the colon
  • Views the anus, rectum and lower third of the colon
  • Takes about 15 minutes
  • Usually performed under anesthesia but can be done while you are awake
  • Screenings are required every five years

Colonoscopy

  • Uses a thin tube and a small camera
  • Requires prep to clean out the colon
  • Views the anus, rectum and entire colon
  • Takes about 30-60 minutes
  • Performed under anesthesia
  • Allows screening interval to be extended to every 10 years

Why might I need a sigmoidoscopy?

Your doctor might perform a sigmoidoscopy if you have symptoms of a condition in your lower digestive tract. The procedure is also used to diagnose colon and rectal cancer or as a follow-up during cancer treatment.

Some symptoms that might lead to a sigmoidoscopy include:

  • Rectal bleeding
  • Changes in bowel habits, such as diarrhea or constipation
  • Unintentional weight loss
  • Abdominal pain or symptoms

Screening for colon and rectal cancer

If you have an average risk of colorectal cancer, the screening guidelines recommend starting routine screenings at age 45. While colonoscopy is the recommended endoscopy procedure to screen for colon cancer and rectal cancer, sigmoidoscopy is an alternative option that may be combined with other imaging tests.

The main disadvantage of sigmoidoscopy for colorectal cancer screening is that your care team can’t view the entire colon. It has to be carried out more frequently. But compared to colonoscopy, it’s a shorter procedure and can be done without anesthesia. Talk with your doctor if you have questions about the right screening for you. 

Female healthcare provider sitting with male patient at an office desk, explaining how to prepare for a sigmoidoscopy.

Preparing for a sigmoidoscopy

Your doctor’s office will give you specific instructions to prepare for your sigmoidoscopy, including diet changes and bowel prep. You’ll also want to let your doctor know about any medications or allergies.

  • Change your diet and clean out your bowel: You’ll need to follow a liquid diet for 24 hours before a sigmoidoscopy—including liquids like water, broth, plain coffee or tea, juices or gelatin. You will also take either prescription or over-the-counter medications to clean out your bowel before the procedure.
  • Medication adjustments: You may need to stop taking some medications, such as blood thinners, diabetes medications or iron supplements, several days before your sigmoidoscopy. Your doctor will tell you what prescriptions, over-the-counter medications and supplements to stop.

The sigmoidoscopy procedure

Doctors perform sigmoidoscopy procedures both in the hospital and as an outpatient procedure. While you'll need to complete your prep before your sigmoidoscopy, the actual procedure itself takes around 15 minutes.

When you schedule your sigmoidoscopy, you'll receive detailed instructions about how to prepare and what to expect. It's important to follow your doctor's instructions carefully so your procedure isn't delayed.

  • Before the procedure

    Before your procedure, you’ll meet members of your care team and can ask any questions. You’ll change into a gown and remove any jewelry. Then, your care team will help you get in the correct position on the exam table, usually lying on your left side.

  • During the procedure

    Most sigmoidoscopy procedures are performed without anesthesia. Your doctor will start with a rectal exam and then gently insert a lubricated scope into your anus, guiding it into the rectum and lower colon. You may feel discomfort, cramping or the need to go to the bathroom when the scope is first inserted. This is normal.

    During the procedure, air is injected to help inflate the colon and improve visibility. This might lead to abdominal discomfort and bloating. Your doctor can take images and tissue samples as they examine the rectum and colon. If any polyps are found, they may be removed.

  • After the procedure

    After your sigmoidoscopy, you’ll typically lie down for a few minutes before you get up from the exam table, but a stay in recovery isn’t needed. You can resume your regular diet and activities after the procedure.

    Because this procedure uses air, it’s normal to have gas pains or pass gas in the hours following your test. You may also notice a small amount of rectal bleeding. If you continue bleeding or have pain after the first day or have signs of an infection like a fever, call your doctor.

What are the risks of a sigmoidoscopy?

Sigmoidoscopy is a routine endoscopic procedure, and it’s considered safe and effective. But like any procedure, there are a few risks of having a sigmoidoscopy. The two most common risks are:

  • Bleeding, especially where a tissue sample or polyp was removed
  • Perforation of the colon, which is a tear or hole

If you have ongoing bleeding or a perforation, there’s a risk that you’ll need another procedure to repair the problem.

Understanding the results

After your sigmoidoscopy, your doctor will provide an overview of the results. If any biopsies or tissue samples were taken during your procedure, it may take a few days to receive the final report from testing in the lab.

Sigmoidoscopy can detect signs of many different digestive conditions. Based on your results, your doctor will work with you to decide your next steps, including any additional testing or treatment if you have a positive result.

  • Negative result: A negative result means that your doctor did not find any signs of a digestive condition during the exam. The tissues in your lower colon, rectum and anus were normal. If you had a sigmoidoscopy as a screening, talk to your doctor about when to come back for your next routine screening.

  • Positive result: A positive result means your doctor found an abnormality in the colon, rectum or anus during your exam. You may need other tests to confirm a diagnosis.

Sigmoidoscopy can help diagnose

Frequently asked questions

  • Can a flexible sigmoidoscopy detect cancer?

    Yes, a flexible sigmoidoscopy can detect cancer or pre-cancerous polyps. It is one of several screening options available to help you detect—and sometimes prevent—colorectal cancer. Talk to your doctor about the right colorectal screening for you.

  • How long does a sigmoidoscopy take?

    A sigmoidoscopy procedure usually takes about 15 minutes for your doctor to perform. Beforehand, you’ll need to set aside about 24 hours for prep. Because this type of exam doesn’t typically require anesthesia, the recovery time is minimal.

  • Is sigmoidoscopy painful?

    Sigmoidoscopy may cause minor discomfort, including cramping or the feeling that you need to go to the bathroom when your doctor inserts the scope. You may also have gas pains from the air that’s injected during the procedure, but this discomfort resolves quickly.

  • When should I stop eating before a sigmoidoscopy?

    On the day before your sigmoidoscopy, you’ll need to stop eating solid foods and follow a clear liquid diet as directed by your care team. Be sure to follow these instructions so your doctor has a clear view during your exam.

    If your sigmoidoscopy is in the morning, you’ll stop eating and drinking at midnight before your procedure. If it’s in the afternoon, your doctor will give you instructions on when to stop eating or drinking.

  • Do you need to fast for a flexible sigmoidoscopy?

    Yes, you’ll typically need to follow a clear liquid diet the day before your sigmoidoscopy and start a complete fast at midnight or several hours before your exam, depending on your scheduled procedure time.