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Get the Facts: Colonoscopy vs. Virtual Colonoscopy

Focused on Health - March 2009

By Adelina Espat

If you’re age 50 or older, you already may know you need to be screened for colorectal cancer, but what exam should you get? Unlike other more common cancers, colorectal cancer has several screening exams from which to choose.

The most widely used screening exam is colonoscopy, which is an accepted, standard screening test. However, many people have concerns about colonoscopy-related complications, such as bleeding and/or tearing of the colon. A newer option, virtual colonoscopy sounds less invasive and may appeal to the public as a more desirable alternate screening tool. Let’s compare the two.

Colonoscopy (every 10 years unless polyps are found) – A doctor uses a colonoscope, a lighted tube, to examine the rectum and colon.


  • Most colorectal cancers begin as a polyp (a small, non-cancerous growth on the colon wall that can grow larger and become cancerous over time). During a colonoscopy, doctors can detect and immediately remove these polyps. Polyp removal is considered the most effective way to prevent the development of colorectal cancer.


  • This test may not detect all small polyps, nonpolypoid lesions (flat and depressed abnormal pieces of tissue), or cancers, but it is one of the most sensitive tests currently available.
  • Thorough cleansing of the colon is necessary before this test. Your doctor may instruct you to take laxatives 24 hours before the test. You also will not be able to eat or drink anything after midnight the night before your test.
  • Some form of sedation is used in most cases. If sedation is used, someone will need to drive you home.
  • Although uncommon, sedation or instrument-related complications, such as bleeding and/or tearing of the colon, can occur.

Virtual colonoscopy (every 5 years) – A health care provider uses specialized CT scan techniques to produce images of the abdomen and pelvis. A computer then assembles these images into detailed, three-dimensional pictures that can show polyps and other abnormalities.


  • It is less invasive than standard colonoscopy.
  • Virtual colonoscopy may be as sensitive as standard colonoscopy if performed in experienced centers.
  • Because sedation is not needed, virtual colonoscopy can be more convenient, does not have sedation-related risks and does not require someone to accompany you to the examination.
  • Risk of instrument-related complications, such as bleeding or tearing of the colon, may be lower than with standard colonoscopy.


  • Like standard colonoscopy, this test may not detect all small polyps, nonpolypoid lesions and cancers.
  • Thorough cleansing of the colon is necessary before this test, similar to what is done to prepare for a colonoscopy.
  • If an abnormality, such as a polyp, is detected, you will need to undergo a standard colonoscopy after the virtual procedure to remove the polyp or lesion, or to perform a biopsy.
  • Because sedation is not used, you may experience some discomfort during virtual colonoscopy when air is pumped into the colon.
  • Virtual colonoscopy exposes the patient to a low dose of radiation (more than a chest x-ray and less than a conventional CT scan).

Study Participants Compare Both Tests

A study, published in the Dec. 4, 2003 issue of The New England Journal of Medicine, compared virtual colonoscopy with standard colonoscopy. Study participants completed both exams. When asked to compare the two techniques, about:

  • 54% of participants said virtual colonoscopy was more uncomfortable
  • 38% said the traditional method was more uncomfortable
  • 8% were undecided

The study’s researchers believe that most participants found virtual colonoscopy more uncomfortable because, unlike colonoscopy, participants were not sedated, causing them to experience some discomfort during the exam.

Source: National Cancer Institute

Based on this information, neither colonoscopy nor virtual colonoscopy is the perfect screening tool. There are advantages and disadvantages for both, and neither is considered 100% accurate in detecting polyps and precancerous changes in the colon and rectum. However, recent research does support both tests as effective screening methods.

A study published in the Jan. 6, 2009 issue of Annals of Internal Medicine concluded that the chances of dying from colon cancer was lower in people who had a colonoscopy, specifically if the cancer was found in the left colon. Another study, published in the Sept. 18, 2008 issue of the New England Journal of Medicine, found that virtual colonoscopy identified 90% of participants with precancerous and cancerous polyps 10 millimeters or more in diameter.

“The take-home message here is that both exams are viable options for testing for the disease, and it’s better to get screened for colorectal cancer than not,” says George J. Chang, M.D., M.S., assistant professor in M. D. Anderson’s Department of Surgical Oncology. “And, the detection rate for these exams improves if you follow the appropriate recommendations for test preparation as well as the suggested screening schedule.”

Scientists are still studying these and other screening exams to learn more about their accuracy and the possible risks of each test. They also are conducting studies to find new and better ways to screen for colorectal cancer.

Your Doctor Can Help You Make the Decision

If you are between the ages of 50 and 75, speak with your health care provider about colonoscopy and virtual colonoscopy, as well as other colorectal cancer screening exams. Discuss the benefits and disadvantages of each test, and how often to obtain these exams.

“Colonoscopy and virtual colonoscopy are not the only tests available to screen for colorectal cancer, but they are currently the most effective single tests,” Chang says.

In September 2008, the American College of Radiology, the American Cancer Society and the U.S. Multisociety Task Force on Colorectal Cancer published updated colorectal screening guidelines. After careful review of various screening exams, the group approved several choices for colorectal cancer screening. In addition to colonoscopy and virtual colonoscopy, the fecal occult blood test (FOBT), fecal immunochemical test (FIT), double contrast barium enema and sigmoidoscopy were supported as effective options to screen for colorectal cancer.

The fecal occult blood test (FOBT) and the fecal immunochemical test (FIT), performed annually, check for hidden blood in the stool. Studies have shown that FOBT, when performed every one to two years, can help reduce the number of colorectal cancer deaths by 15 to 33%, according to the National Cancer Institute. The FIT detects about 81% of colorectal cancers and about 29% of polyps and nonpolypoid lesions.

The sigmoidoscopy, performed every five years, examines the rectum and lower colon using a lighted instrument called a sigmoidoscope. Similar to the colonoscopy, precancerous and cancerous polyps in the rectum and lower colon can be found and removed.

The double contrast barium enema (DCBE) is performed every five years. During this exam, the patient is given an enema with a barium solution and air is pumped into their colon. A series of x-rays is then taken of their colon and rectum. This exam detects about 30 to 50% of the cancers found with traditional colonoscopy, according to the National Cancer Institute.

Depending on your risk factors, health history and insurance coverage, your health care provider may recommend one of these tests and an examination schedule.

Below are additional screening schedule issues to discuss with your health care provider:

  • If you have a family history of colorectal cancer or a personal history of inflammatory bowel disease, you may need to start colorectal cancer screening before age 50.
  • If you are over age 75 and in good health, you may still need to continue colorectal cancer screening.

You also should ask your health insurance provider about what colorectal screening exams are covered under your benefits. Not all providers cover the costs of a virtual colonoscopy.

Get Screened!

“Colorectal cancer screening exams are a vital weapon in the war against cancer,” Chang says. “Unlike other screening exams, such as the mammogram, which primarily detects cancer, often at an earlier, more treatable stage, colorectal screening exams also can be used to prevent the disease by detecting and removing polyps before they develop into cancer.”

Fortunately, more and more people are getting screened for colorectal cancer. However, even with these improvements, colorectal cancer screening rates still remain low. “Many people don’t get screened because they either are not aware of the importance of screening or are embarrassed about doing the exam,” Chang says. “Others may just not want to do all the steps required to prepare for a colonoscopy.”

In 2005, 59% of people 50 and older got a colorectal cancer exam. This includes 40% of Hispanics, 52% of Blacks and 61% of Whites. Among Asian women interviewed in California, 60% had used a colorectal cancer test.

Source: National Cancer Institute

“The reason for Colorectal Cancer Awareness Month in March is to get people talking about the importance of screening,” Chang says.

Colorectal cancer is the third most common cancer in this country and affects men and women equally. Almost 150,000 people in the U.S. were expected to be diagnosed with colorectal cancer during 2008, according to the American Cancer Society. Colorectal cancer also is the second leading cause of cancer death among Americans, with about 50,000 deaths expected in 2008. With wider use of cancer screening exams, colorectal cancer can be considered a highly preventable disease.

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