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 with a scope inserted into the rectum or with special x-ray tests. Polyps found before they turn into cancer can be removed, so these tests may prevent colorectal cancer. Because of this, they 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. Before the test, you will need to take some medicine to clean out your colon. If a small polyp is found your doctor may remove it during this test. 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.

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.

Before the test: The colon and rectum must be empty and clean. You will need to 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 them step by step with the nurse. 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 may 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.

You may need to have someone drive you home from the test because the medicine used can affect your ability to drive. Some doctors require that someone drive you home.

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 similar to that for the colonoscopy (above), although for the DCBE you will not be given drugs to make you sleepy.

Virtual colonoscopy: You might think of this as a super x-ray or 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 part of your body being studied. Virtual colonoscopy ( also calledCT 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 such as colonoscopy. It can be done fairly quickly and you do not need sedation. But while this test is not invasive like colonoscopy, it still requires 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 explore them fully.

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 to be 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 such as colonoscopy.

These tests have different names such as FOBT, FIT, and iFIT. 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.

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 the following:

• 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 aspects of 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.

Insurance coverage for colorectal cancer screening

Although there are good colorectal cancer screening tests, not enough people have them done. Some of the reasons could include the lack of awareness of screening tests, costs, and lack of health insurance coverage and/or benefits.

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 separate American Cancer Society document, Colorectal Cancer: Early Detection.

How is colorectal cancer diagnosed?

Most people with early colon cancer don’t have symptoms. Symptoms usually appear with more advanced disease. If something suspicious turns up as a result of screening or if you have symptoms, you will need further tests.

Signs and symptoms of colorectal cancer

• a change in bowel habits such as diarrhea, constipation, or narrowing of the stool that lasts for more than a few days 
• a feeling that you need to have a bowel movement that doesn't go away after doing so 
• rectal bleeding, dark stools, or blood in the stool (often, though, the stool will look normal) 
• cramping or stomach pain 
• weakness and tiredness.

Most of these symptoms are more likely to be caused by something other than colorectal cancer. Still, if you have any of these problems, it's important to see your doctor right away so the cause can be found and treated, if needed.

If there is any reason to suspect colon or rectal cancer you will need to have more tests to find out if the disease is really present and, if so, to see how far it has spread. Some of these tests are the same ones that are used for screening people who do not have symptoms. (See the section below, "Tests to look for colorectal polyps and cancer.")

Medical history and physical exam: Your doctor will ask you questions about your health, your family history, and she will also do a complete physical exam.

Blood tests

Your doctor may order certain blood tests to help find out if you have colorectal cancer. People with colorectal cancer often become anemic because of bleeding from the tumor. You might also have blood tests to check your liver function because colorectal cancer can spread to the liver. There are other substances (tumor markers) in the blood that can help tell how well treatment is working. But these tumor markers are not used to find cancer in people who have not had cancer and who appear to be healthy. They are most often used for follow-up of people who have already been treated for colorectal cancer.

Tests to look for colorectal polyps or cancer

If symptoms or the results of the physical exam or blood tests suggest that you might have colorectal cancer, your doctor may want to do some more tests.

Biopsy: In a biopsy, the doctor removes a small piece of the tissue that does not look normal. This is done during a colonoscopy. The tissue is sent to the lab where it is looked at under a microscope to see if cancer is present. While other tests may suggest colorectal cancer, a biopsy is the only way to know this for sure.

Imaging tests

These tests, described below, make pictures of the inside of your body. Imaging tests may be done for a number of reasons, such as to help find out whether a suspicious area might be cancer, to learn how far cancer may have spread, and to help learn if treatment is working.

Computed tomography (CT or CAT) scan

A CT scan uses x-rays to take many pictures of the body that are then combined by a computer to give a detailed picture. A CT scan can often show whether the cancer has spread to the liver, lungs, or other organs. CT scans take longer than regular x-rays. The patient has to lie still on a table while the CT scan is being done. A contrast "dye" may be injected or a special drink used to help outline the area being viewed.

CT scans can also be used to guide a biopsy needle into a tumor or metastasis. For this to be done, the patient remains on the CT table, while a radiologist moves a biopsy needle through the skin and toward the mass. A tiny fragment of tissue or a thin cylinder of tissue about ½ inch long and less than 1/8 inch wide is then removed and looked at under a microscope.

A new way to use a CT scan is to do a "virtual colonoscopy." After stool is cleaned from the colon and the colon is filled with air, a computer can then put together a picture of the inside of the colon. This method requires the same preparation as for a colonoscopy and there is some discomfort from the bowel being filled with air. If anything not normal is seen, a follow-up colonoscopy will be needed.

Ultrasound

Ultrasound uses sound waves to produce a picture of the inside of the body. Most people know about ultrasound because it is often used to look at a baby during pregnancy. This is an easy test to have. You simply lie on a table while a kind of wand is moved over your skin.

Two special types of ultrasound might be used for people with colon or rectal cancer. In one, the wand that gives off sound waves is placed into the rectum to look for cancer there and to see if it has spread to nearby organs or tissues. In the other test, used during surgery, the wand is placed against the surface of the liver to see if the cancer has spread there.

Magnetic resonance imaging (MRI) scan

Like CT scans, MRIs show a cross-section of the body. But, MRI uses radio waves and strong magnets instead of radiation to take pictures. As with CT scans, a contrast dye may be injected, although this is used less often. MRI scans are helpful in looking at the brain and spinal cord. They take longer than CT scans and you may have to be placed inside a narrow tube for the test. This can feel confining and upset people with a fear of closed spaces. The machine also makes a thumping noise, but some places will provide headphones with music to block this out.

Chest X-ray

This test may be done to see whether colorectal cancer has spread to the lungs.

Positron emission tomography (PET) scan

In this test, a type of radioactive sugar is injected into a vein. Then you are put into the PET machine where a special camera can detect the radioactivity. The cancer cells absorb high amounts of the sugar and show up on the pictures as dark "hot spots." PET is useful when your doctor thinks the cancer has spread, but doesn't know where. PET scans are now more accurate because they can be combined with a CT scan.

Angiography

For this test, a tube (called a catheter) is placed into a blood vessel and moved until it reaches the area to be studied. Then a dye is injected and a series of x-ray pictures is taken. When the pictures are done, the catheter is taken out. Surgeons sometimes use this to find blood vessels next to cancer that has spread to the liver. The cancer can then be removed without causing a lot of bleeding.