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Flexible sigmoidoscopy

Examines your rectum and lower part of the colon with a lighted tube called a sigmoidoscope.

  • Can find cancer in earliest stage, when most treatable
  • Complications are rare
  • Less expensive option to colonoscopy


  • Can identify polyps before they turn into cancer
  • Usually does not require sedation and takes only about 20 minutes
  • Moderate cost; covered by most insurance
  • Many primary care providers can do the test in their office
  • Can accurately find polyps in the lower part of the colon (where most polyps occur)


  • Not all polyps can be removed during the procedure but they can be biopsied; will need to get a colonoscopy if biopsy is positive for colorectal cancer
  • Requires enema preparation
  • Patients may find test uncomfortable or embarrassing
  • Small risk of perforation or bleeding
  • Does not examine the first half of the colon (the portion of the colon farthest from the anus)

What can I expect for a bill?

Average cost before insurance: $500 – $750

Average cost people pay: $150 – $300

Will my insurance cover it?

Many insurance plans cover the screening test every four to five years starting at age 50. Medicare covers it once every four years; you pay 20% of the Medicare-approved amount after Part B deductible.

The facts

Flexible sigmoidoscopy, or flex sig, is a procedure used to see inside the sigmoid colon (the last one-third of the colon) and rectum (which connects the sigmoid colon to the anus). Here’s how it works: your doctor inserts a flexible tube (about the thickness of a finger) into the anus and slowly advances it into the rectum and lower part of the colon. Your doctor can detect inflamed tissue, abnormal growths and ulcers. This screening method is used to look for early signs of cancer and can help doctors diagnose unexplained changes in bowel habits, abdominal pain, bleeding from the anus and weight loss.

The prep

Preparation for flex sig can vary. Some doctors will recommend one or more enemas before the procedure, others will recommend a clear liquid diet for 1-3 days, while others will advise you to forgo any prep. Your doctor will tell you the specifics on what will be the best prep method for you.

The procedure

So here’s what everyone wants to know: what’s actually going to happen to me during a flex sig? To start the procedure, you will lie on your left side on an exam table. Your doctor then inserts a long, flexible, lighted tube called a sigmoidoscope, or scope, into the anus and slowly guides it through the rectum and into the sigmoid colon. The scope inflates the colon with air to give the doctor a better view. A tiny camera mounted on the scope transmits a video image from inside the colon to a computer screen, allowing the doctor to carefully examine the tissues lining the sigmoid colon and rectum.

You may be asked to move periodically so the scope can be adjusted for better viewing. The lining of your colon is then examined again as the scope makes its way out. You may experience a feeling of pressure, bloating or cramping during the procedure, but this will quickly subside once the air passes out of you. And the best part: as soon as the procedure is finished, you can get dressed, leave on your own, drive and resume your normal diet and activities right after.

The big 'what if…'

If your doctor sees an area of your colon that needs further evaluation, he or she may take a biopsy to be analyzed. Biopsies are used to identify many conditions, and your doctor may order one even if cancer isn’t suspected.

If small polyps are found, they may be removed using special tools passed through the scope. Larger polyps, too big to remove during the procedure, can be biopsied and tested for colorectal cancer. If a biopsy taken during a flex sig comes back positive for colon cancer, you will need a colonoscopy to remove that polyp.

After the test

Flex sig and biopsies are safe when performed by doctors specially trained and experienced in these procedures. Complications are rare, but it’s important you recognize early signs in case they do arise. Contact your doctor if you experience severe abdominal pain, fevers and chills, dizziness or rectal bleeding. Note that rectal bleeding can occur several days after the exam.

How often (if not high risk)

Every 5 years starting at age 45.

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