Colorectal cancer screening tests

Screening tests are used to look for disease in people who do not have any symptoms. In many cases, these tests can find colorectal cancers at an early stage and greatly improve the chances of successful treatment. Screening tests can also help prevent some cancers by allowing doctors to find and remove polyps that might become cancer. The tests used to screen for polyps and colorectal cancer can be divided into 2 broad groups:

• Tests that can find both colorectal polyps and cancer: These tests are done either by looking at the colon using a scope that is put into the rectum, or with special x-ray tests. Polyps found before they become cancer can be removed, so these tests may prevent colorectal cancer. Because of this, these tests are preferred if they are available and you are willing to have them.

• Tests that mainly find cancer: These involve testing the stool (feces) for signs of cancer. These tests are easier to have done, but they are less likely to find polyps.

Tests that can find both colorectal polyps and cancer

Flexible sigmoidoscopy (flex-sig): A sigmoidoscope is a thin, flexible, lighted tube about the thickness of a finger. It is placed into the lower part of the colon through the rectum. This allows the doctor to look at the inside of the rectum and part of the colon for cancer or polyps. Because the tube is only about 2 feet long, the doctor is only able to see about half of the colon. The test can be uncomfortable, but it should not be painful. Be sure your doctor is aware of any medicines you are taking, as you may need to change how you take them before the test.

Before the test, you will need to take some medicine to clean out your colon and rectum. This is so the doctor can clearly see the lining. If a small polyp is found your doctor may remove it during this test. This can be done with tools used through the scope. If an adenoma polyp or colorectal cancer is found during the flex-sig, you will need to have a colonoscopy to look for polyps or cancer in the rest of the colon.

A sigmoidoscopy usually takes 10 to 20 minutes. Most people do not need to be sedated for this test, but this may be an option you can discuss with your doctor. Sedation may make the test easier, but you will need some time to recover, as well as someone with you to take you home after the test.

Colonoscopy: A colonoscope is a longer version of the sigmoidoscope. It is used the same way but allows the doctor to see the entire colon. If a polyp is found, the doctor may remove it. If anything else looks abnormal, a biopsy might be done. To do this, a small piece of tissue is taken out through the colonoscope. The tissue is sent to the lab to see if cancer cells are present.

Colonoscopy may be done in a hospital outpatient department, in a clinic, or in a doctor's office.

Before the test: The colon and rectum must be empty and clean. You will take some medicine to clean out your colon the day before the test and maybe an enema that morning. Your doctor will give you exact instructions. Be sure to read these carefully a few days ahead of time, since you may need to shop for special supplies and get laxatives from a drug store. If you are not sure about anything, call the doctor's office and go over things step by step with the nurse.

Be sure your doctor is aware of any medicines you are taking, as you may need to change how you take them before the test. Many people find the bowel preparation to be the most unpleasant part of the test, as you will most likely be in the bathroom quite a bit. You may be given other instructions, too, such as foods to avoid for a certain amount of time before the test.

During the test: The test itself usually takes about 30 minutes, but it may take longer if a polyp is found and removed. Before the test begins, you will be given medicine through your vein to make you feel comfortable and sleepy. You may be awake, but you will not be aware of what is going on and may not remember the test afterward. Most people will be fully awake by the time they get home from the test.

If a small polyp is found, the doctor may remove it. If your doctor sees a larger polyp or tumor or anything else not normal, a biopsy may be done. To do this, a small piece of tissue is taken out through the colonoscope. The tissue is looked at under a microscope to see whether it is a cancer, a benign (non-cancer) growth, or a result of inflammation.

After the test: You may need to have someone drive you home from the test because the medicine used can affect your ability to drive. Your doctor will tell you if you need someone to drive you home. Some people may have gas pains or cramping for a while after the test, but most feel fine once the drugs wear off.

Double contrast barium enema (DCBE): To do this test a chalky substance is used to partly fill and open up the colon. Air is then pumped in to cause the colon to expand. This allows good x-ray pictures to be taken. If an area does not look normal you will need to have a colonoscopy.

The preparation for this test is much like that for the colonoscopy (above), but for the DCBE you will not be given drugs to make you sleepy. It takes about 30 to 45 minutes to do this test. A small, flexible tube is put into the rectum, and barium sulfate is pumped in to partly fill and open up the colon. When the colon is about half-full of barium, you are turned on the x-ray table so the barium spreads throughout the colon. Then air is pumped into the colon through the same tube. This may cause discomfort and you may feel like you have to have a bowel movement. You may have bloating or cramping after the test, and will likely feel the need to empty your bowels soon after the test is done. The barium can cause constipation for a few days, and your stool may look grey or white until all the barium is out.

Virtual colonoscopy: You might think of this as a super x-ray or an advanced CT scan of the colon. The CT scanner takes many pictures as it rotates around you while you lie on a table. A computer then combines these pictures into images of slices of the colon and rectum. Virtual colonoscopy (also called CT colonography) involves the use of special computer programs to create both 2 dimensional x-ray pictures and a 3-D "fly-through" view of the inside of the colon and rectum, which allows the doctor to look for polyps or cancer.

This test may be useful for some people who can't have or don't want to have tests where a tube or scope is put in the colon or rectum. It can be done fairly quickly and you do not need drugs to make you sleepy. But while this test does not mean a scope will be put into your colon like colonoscopy, you still need to do the same type of bowel preparation. If polyps or other problems are seen on this test, a colonoscopy will likely be needed to remove them or to get a better look at them.

Tests that mainly find colorectal cancer

These tests are used to find small amounts of hidden (occult) blood in the stool. Most people find these tests are easier because they can often be done at home. But they are not as good at finding polyps as the tests described above, and a positive result on one of these screening tests will likely mean you will need a test like a colonoscopy.

These tests have different names such as FOBT (fecal occult blood test), FIT (fecal immunochemical test), and iFOBT (immunochemical fecal occult blood test). They are all alike in that you will need to collect samples of your stool (bowel movement) to be sent to a lab for testing. They differ in the exact way in which you collect the samples and in how the samples are studied in the lab.

If you are having one of these tests, the doctor or nurse will give you a kit with exact instructions on what to do ahead of time (there may be some limits on what you can eat or drink or medicines that you take) and how to collect the samples.

Some people who are given the kits never do the test or don't give it to their doctor because they worry that they might not have followed the instructions right. Be sure to talk to your doctor or nurse if you have any questions about what you should do or how to collect the samples. The most important thing is to get the test done.

Most of these tests need to be done every year, and, as mentioned before, if the lab spots any problems, you will need to have more tests such as a colonoscopy. For more detailed information about these tests, please see, Colorectal Cancer: Early Detection.

Preventing colorectal cancer or finding it early

Colon cancer begins with a growth (a polyp) that is not yet cancer. Testing can help your doctor tell whether there is a problem, and some tests can find polyps before they become cancer. Most people who have polyps removed never get colon cancer. If colon cancer is found, you have a good chance of beating it with treatment if it is found early. Testing can find it early.

The American Cancer Society believes that preventing colorectal cancer (and not just finding it early) should be a major reason for getting tested. Finding and removing polyps keeps some people from getting colorectal cancer. Tests that have the best chance of finding both polyps and cancer should be your first choice if these tests are available to you and you are willing to have them.

Doctors will take into account a number of factors when they recommend the tests you should have, how often you should have them, and when you should begin testing. These factors include whether you are at average, increased, or high risk for colorectal cancer. If you are at increased or high risk, the type of test used and how often it is done will further depend on whether you have had polyps, cancer, or certain other diseases, as well as your family history.

In general, both men and women at average risk of colorectal cancer should begin screening tests at age 50. But you should talk with your doctor about your own health and your family history so that you can choose the best screening plan for you. For more detailed information about the American Cancer Society's recommendations for screening, please see our document, Colorectal Cancer: Early Detection.

Insurance coverage for colorectal cancer screening

There are good colorectal cancer screening tests, but not enough people have them done. Some of the reasons could include not knowing about screening tests, costs, and lack of health insurance.

Laws regarding insurance coverage for colorectal cancer screening tests vary by state. The same is true of state Medicaid programs. For people with Medicare, coverage begins at age 50 for the most common colorectal cancer screening tests.

For more information on insurance coverage for colorectal cancer screening tests, please see the our document, Colorectal Cancer: Early Detection.

Last Medical Review: 03/05/2008
Last Revised: 05/07/2009