A colonoscopy is a visual examination of the rectum and the entire colon with a thin, flexible tube attached to a lighted video camera (colonoscope). It is the most sensitive test for diagnosing certain conditions, such as polyps, ulcers, pouches (diverticulosis) and narrowed areas (strictures). It is also used to detect colorectal abnormalities such as precancerous and cancerous growths

The colon is another term for the large intestine, the last portion of the digestive tract, which also includes the esophagus, stomach and the small intestine. The colon measures approximately 3 to 5 feet long (0.91 to 1.52 meters). It starts at the cecum (attached to the end of the small intestine) and ends at the rectum and anus. The colon’s most important job is to dry, process and store food products that are not absorbed into the body. Eventually, this waste is eliminated during defecation.

Colonoscopies capture images that are more sensitive than those provided by x-rays. In addition, colonoscopies can be used for treatment as well as diagnosis for some conditions. For example, in a patient with polyps, a physician can pass surgical instruments through a colonoscope to remove growths that can then be analyzed by a pathologist.

A colonoscopy may be used to diagnose many different disorders of the colon and rectum. A physician may recommend the test if other screening tests indicate a potential problem. These screening tests include a digital rectal examination (during which a physician examines the rectum with a gloved finger), a fecal occult blood test (FOBT) and a barium enema.

A colonoscopy can be used to:

• Identify the location or cause of bleeding in the colon
  
  
• Check for areas of irritation or sores in the colon
  
  
• Diagnose any inflammatory digestive diseases, such as Crohn's disease or ulcerative colitis, that cause symptoms including pain, bloody diarrhea and weight loss
  
  
• Help determine the cause of unexplained changes in weight or bowel habits (e.g., diarrhea)

However, colonoscopies are used most often as a screening tool for colorectal cancer. The American Cancer Society (ACS) recommends that beginning at age 50, all men and women should participate in at least one of the five following screening options:

• Yearly fecal occult blood test (FOBT) or fecal immunochemical test (FIT)
  
  
• Flexible sigmoidoscopy every five years
  
  
• Combination of yearly FOBT/FIT and flexible sigmoidoscopy every five years (preferred by ACS)
  
  
• Double contrast barium enema every five years
  
  
• Colonoscopy every 10 years

In addition, patients younger than 50 with a higher risk of colon cancer should consider a colonoscopy or alternate form of colorectal screening test. This group may include individuals with a family history of colorectal cancer or patients who have been previously treated for colon polyps. It may also include patients who have been diagnosed with another form of cancer. Research also suggests that people who smoke cigarettes and drink heavily may benefit from earlier screening as they often develop colorectal cancer at a younger age than those who refrain from using these substances. 

Colonoscopies present little risk or discomfort to the patient.  However, the success of a colonoscopy largely depends on the patient’s willingness to follow a physician’s instructions on cleaning out the colon prior to the procedure. This may include the use of laxatives or enemas that some patients find uncomfortable or disruptive.

Research indicates that many Americans over the age of 50 fail to receive regular colonoscopies. In fact, a recent study in the United States found that nearly half of over 21,000 patients seen by primary care physicians did not receive a colorectal screening even though it was recommended.

Despite the inconvenience and discomfort, colonoscopies continue to be the best technique for detecting colorectal abnormalities and saving lives.

A newer version of the procedure, called virtual colonoscopy (VC), uses a CAT scan or MRI with computer software to create very detailed x-ray images of the colon and rectum. The test is less invasive than a traditional colonoscopy but has limitations. VC is not as detailed as conventional colonoscopy and may miss small polyps. Also, if a polyp is found with VC, a conventional colonoscopy is still necessary to remove the growth. Studies comparing the two techniques to more traditional colonoscopies have yielded mixed results. The technology is improving, and virtual colonoscopies show promise for the future. However, at this time, the ACS does not recommend VC as a screening tool for early detection of colorectal cancer. VC requires the same pre-procedure colon preparation that is necessary for standard colonoscopy.