Proceedures Involved in Colon Cancer Screening

Colon cancer is the second leading cause of cancer death in the United States. Sometimes referred to as colorectal cancer, up to one third of people diagnosed with this cancer will die from it. Because of this very high mortality rate, extensive screening guidelines have been developed in an effort to detect colon cancer as early as possible, when treatments can be most effective.

Screening for colon cancer allows detection of the disease before symptoms appear. In addition, there are some screening procedures which can actually double as minor treatments, such as the removal of benign polyps, which can eventually turn cancerous. Current guidelines suggest that all people begin screening for colon cancer at age 50. An overwhelming majority of colon cancer develops after this age. In select high risk populations, screening procedures may begin as young as age 40.

Several factors go into making an effective screening test for colon cancer (or any other disease). The test must be sufficiently sensitive. This means that the test must be able to detect a vast majority of cases of colon cancer. A test which misses most cancers is useless. In addition, the test must be specific. A test which is positive in a wide range of different conditions is not as useful as one which is positive for only one disease.

A good screening test must also entail as little risk to the patient as possible. Cost of the screening procedure is a factor as well. Lastly, the screening test must be able to detect the potential cancer at a very early stage, when something can still be done to effectively treat it.

Because most cases of colon cancer take many years to develop to a serious level, screening can be quite effective in lowering mortality. Some screening techniques have been shown to lower risk of developing colon cancer caused by certain factors by up to 90%.

There are currently four major screening tests for colon cancer. Each of them has specific advantages and disadvantages. This review is meant to be a quick introduction to each test. For more detailed information about each screening test, and its appropriateness to your health, you should speak with your doctor.

Fecal occult blood testing

The first screening test for colorectal cancer is fecal occult blood testing. Many colon cancers will cause some degree of bleeding. Often this blood is very small and quantity and can be hard to see by just looking at your stools. The fecal occult blood test is a way to detect very small amounts of blood in your stool which would otherwise be impossible to see.

The fecal occult blood test is relatively simple and noninvasive to the patient. The patient being tested is given a set of three credit card size, chemically treated paper cards. Each card has room for two small stool samples. Each stool sample is a very small smudge. The cards are then folded up, sealed properly, and sent to a lab for testing. Picking small samples of your stools out of the toilet may be gross, but the test is relatively simple and straightforward compared to the others.

The major disadvantage to fecal occult blood testing is the very high number of false positive results. Only about 3-5% of positive results will ultimately lead to colon cancer. This is because there are many possible causes of blood in the stool, not just colorectal cancer. A positive fecal occult blood test does not mean you have, or ever will have, colon cancer. Further testing is indicated in most cases.

Barium enema

A barium enema is another screening test for colon cancer. The most accurate and commonly done version of this test is actually known as a double-contrast barium enema.

This test is a special x-ray which takes a picture of the entire colon and rectum. Before the x-rays taken, a liquid solution containing barium is injected into your rectum. The liquid will coat the inside of your bowels, and is drained out before the x-ray is taken. The coating which remains shows the lining of the bowels on the x-ray in fine detail.

Double-contrast barium enemas are able to detect about 40 to 50% of precancerous polyps in the tested area. The test itself is safe, although a bit uncomfortable for the patient. The effectiveness of a barium enema in reducing deaths from colon cancer is somewhat controversial. Data on its effectiveness is mixed. In addition, positive tests are usually followed up with a colonoscopy (discussed below).


Sigmoidoscopy is the first of two screening tests for colon cancer which allow a doctor to have a direct view of the inside of your bowels. The procedure involves inserting a small, flexible fiber-optic tube into the lower part of your colon. In medical jargon the test is often referred to as a “flex sig”.

The tube which is inserted has a small camera on the end which is hooked up to a TV monitor. This allows the doctor to take video and pictures of the inside of your bowels.

A flexible sigmoidoscopy does not look at the entire large intestine. It only looks at about half of the total area of colon and rectum. There is minimal risk involved in flexible sigmoidoscopy. In rare cases, it is possible for the camera to cause a small puncture or tear in the lining of the intestine. The most significant disadvantage to the screening test is that it does not look at the entire large intestine.


Colonoscopy is very similar to sigmoidoscopy, only it is more invasive and allows the doctor to see the entire large intestine. Colonoscopy also allows a doctor to remove some small polyps, which are can be precancerous. Colonoscopy uses a similar camera to the flex sig, only it is now a little larger and longer.

Because this procedure can be uncomfortable for the patient, a mild sedative is given to keep the patient as calm and relaxed as possible.

Colonoscopy has an excellent ability to detect just about any lesion which may be cancer or precancerous. The doctor is able to see the entire colon and rectum during this exam. With this increased sensitivity comes some increased risk. The tube used to do the exam can puncture the wall of the bowel, and sedation used can have side effects as well.

You should work with your doctor to develop a screening plan and assess your risk for colon cancer. Each of these tests are important in the process of early detection for colon cancer, however you must work with your doctor to determine which of them may be most appropriate for you. If you have specific questions about the details of any of these exams, speak with your doctor as well.