What are colorectal cancer screening tests?

Colorectal cancer screening tests check for colorectal cancer before you have any symptoms. Colorectal cancer is a type of cancer that affects the colon or rectum. The colon makes up most of the large intestine. The rectum is at the end of the large intestine and connects to the anus.

Colorectal cancer screening can help to:

• Find colorectal cancer early, when treatment is most effective.
• Prevent cancer from developing. Some screening tests let your health care provider find and remove abnormal growths, known as colorectal polyps. Cancer in the colon or rectum often starts as a polyp. Most of these polyps are benign (not cancerous) but could become cancerous if not removed.
• Find bleeding that you can't see, which may mean you have a polyp.

Other names: colon cancer screening

What are they used for?

Colorectal cancer screening tests are used to check for signs of colorectal cancer and remove any colorectal polyps.

Why do I need a colorectal cancer screening test?

Regular screening can detect colon polyps and colorectal cancer. If you aren't at higher risk for colorectal cancer, your provider will likely recommend you start screenings at age 45. If you are at higher risk, you may need to start getting screened for colorectal cancer earlier. Talk with your provider about when to start, how often to get screened, and which type of test you should have.

You may need to be screened at a younger age, or more often, if you have certain risk factors, including:

• A family history of colorectal cancer
• A personal or family history of ovarian cancer
• An inflammatory bowel disease such as ulcerative colitis or Crohn's disease
• Being overweight or having obesity
• Smoking tobacco products
• Alcohol misuse

Some of the tests used to screen for colorectal cancer may also be used as diagnostic tests. They can help your provider make a diagnosis when you are having symptoms of a colonic disease.

What happens during a colorectal cancer screening?

There are two main types of colorectal cancer screening tests: visual exams and stool tests. There are different options for both types of tests.

Visual exams

Visual exams are procedures that allow your provider to look inside your colon and rectum. They are done using a thin tube with a camera attached or a special imaging device. They usually require some type of bowel prep to clear the stool out of your colon. If you need a bowel prep, your provider will give you instructions on how to do it.

Types of visual exams include:

Colonoscopy. This test lets your provider view your entire rectum and colon (large intestine). It is often done in the outpatient department of a hospital or medical center. The procedure takes about 30 to 60 minutes.

Before the test, you will need to empty your colon (large bowel) in a procedure called bowel prep.

During the test:

• You will lie on an exam table.
• You will be given a medicine called a sedative to help you relax and prevent you from feeling pain during the procedure. You may be awake for the test but probably won't remember anything.
• A colonoscope, a thin, lighted tube with a camera attached, will be inserted into your rectum and up into your colon.
• The scope inflates your large intestine with air for a better view. The camera sends a video image to a monitor so your provider can see your colon.
• Your provider will look for colorectal polyps or other abnormal areas.
• If you have polyps, your provider may remove them or tissue samples using special tools inserted through the scope.
• Polyps or samples may be sent to a lab for testing. Most polyps aren't cancer, but removing them can prevent them from becoming cancer later on.
• If you have abnormal tissue, your provider may do a biopsy.

The sedative may make you drowsy for several hours. You should arrange for someone to take you home.

Sigmoidoscopy. This test allows your provider to look at your rectum and the lower colon (sigmoid colon). During the test:

• You will lie on an exam table with your knees drawn up to your chest.
• A sigmoidoscope, a flexible, lighted tube with a camera, will be inserted into your rectum and up into the lower part of your colon.
• Air will be pumped through the sigmoidoscope to make your colon bigger and easier to see.
• The air may make you feel like you need to have a bowel movement or pass gas.
• Your provider may remove polyps or tissue samples using special tools inserted through the scope.
• Polyps or samples may be sent to a lab for testing.

Virtual Colonoscopy. This test is also called a computerized tomography (CT) colonography. It uses x-rays and a computer to take detailed, 3-dimensional pictures of the entire colon and rectum. Since this is an x-ray, this test is not recommended if you are pregnant. Tell your provider if you have any implanted medical devices, such as a pacemaker.

This test is usually done in the radiology department of a hospital or medical center and takes about 10 to 15 minutes. A virtual colonoscopy might be done if you can't have a colonoscopy due to medical reasons. This procedure also requires bowel prep beforehand. During the test:

• You will lie on a narrow table.
• You may be asked to drink a liquid containing contrast dye. Contrast dye is a substance that makes parts of your body show up more clearly on an x-ray.
• A provider will insert a small tube into your rectum.
• Air will be pumped through the tube to make your colon bigger and easier to see.
• The table will slide into the CT machine. This is a tunnel-shaped device where the technician takes the x-ray images.
• You may be asked to hold your breath a few times during the test.
• You will turn over on your side or stomach to get more images taken.
• A series of images will be taken.

You may have some cramping or bloating for about an hour after the test.

Stool tests

Stool tests look at stool samples for blood or other signs of cancer you can't see. But you can also have blood in your stool if you have a health condition that isn't cancer, such as hemorrhoids. Your provider usually prescribes the test, which can be done at home. You take a stool sample and send it to a lab.

Types of stool tests include:

Fecal occult blood tests (FOBT). These tests look for hidden (known as occult) blood in your stool. Blood in the stool may be a sign of polyps, cancer, or other conditions. This test can check if there is blood in your stool, but the test can't tell your provider what is causing the bleeding. Your provider will give you a kit that includes instructions on how to do the test.

There are two types of fecal occult blood tests: the fecal immunochemical test (FIT) and the guaiac smear method (gFOBT). Below are typical instructions for each test. Your instructions may vary slightly, depending on the manufacturer of the test kit.

For a fecal immunochemical test (FIT), you will most likely need to:

• Collect multiple samples from one bowel movement.
• Collect the sample from the toilet using the special brush or other device included in your kit.
• For each sample, use the brush or device to take the sample from the stool's surface.
• Brush the sample onto a test card.
• Label and seal all your samples as directed.
• Mail the samples to your provider or lab.

For a guaiac smear test (gFOBT), you will most likely need to:

• Collect samples from three separate bowel movements.
• For each sample, collect the stool and store it in a clean container. Make sure the sample does not mix in with urine or water from the toilet.
• Use the applicator from your test kit to smear some of the stool on the test card or slide, which is also included in your kit.
• Label and seal all your samples as directed.
• Mail the samples to your provider or lab.

Stool DNA test (FIT-DNA test). This test checks for genetic changes in your stool that may be signs of colorectal polyps or cancer. Your provider will let you know to get a test kit. The kit will include instructions on how to do the test. The instructions will likely include the following steps:

• Put a special container inside your toilet.
• Collect an entire bowel movement.
• Close and seal the container.
• Mail the container with the stool sample to a lab for testing.

Will I need to do anything to prepare for the test?

There are no special preparations needed for a FIT or stool DNA test. The typical preparations for other colorectal cancer screening tests are below.

For a colonoscopy and virtual colonoscopy, you will need to do a bowel prep. Your provider will give you specific instructions on how to do your bowel prep, but steps for bowel prep may include:

• Following a liquid diet for one to three days before the test.
• Drinking plenty of clear liquids one to three days before the test. Clear liquids include water, black coffee or tea, fat-free broth, and sports drinks without added color. Avoid red or purple drinks or gelatin; the dye in those can look like blood in the colon.
• Drinking a strong liquid laxative (a medicine used to cause a bowel movement), taking laxative pills, and/or using an enema on the evening before your test.

The laxative or enema will cause diarrhea. Be prepared to stay close to a bathroom. Bowel prep can be inconvenient and uncomfortable, but if the colon is not thoroughly cleaned out, your provider may not be able to get a complete picture of your colon and rectum. They might not be able to see if you have polyps and other abnormal areas.

Also, you may need to stop taking certain medicines before these tests, so tell your provider about everything you take. But don't stop taking any medicines unless your provider tells you to.

For a sigmoidoscopy, before the test, you may need to:

• Follow a clear liquid diet one or more days before the procedure. This isn't always required, so be sure to talk to your provider before the test.
• You may be asked to fast (not eat or drink) on the morning of the procedure.
• You may need to take a laxative (a medicine used to cause a bowel movement) the night before the test.
• You should empty your bowels with an enema about one hour before the procedure. A second enema is sometimes needed.
• Also, you may need to stop taking certain medicines before these tests, so tell your provider about everything you take. But don't stop taking any medicines unless your provider tells you to.

For a g(FOBT) test, you may need to avoid the following foods and medicines for several days before your test:

• Nonsteroidal, anti-inflammatory drugs (NSAIDs), such as ibuprofen, naproxen, or aspirin
• Vitamin C daily from supplements, fruit juices, or fruit
• Certain vegetables, such as broccoli and turnips
• Red meat, such as beef, lamb, or pork

Your provider will give you full instructions on how to prepare for your screening test.

Are there any risks to the test?

There are no risks to having a fecal occult blood test or a stool DNA test.

Serious risks of colonoscopy are rare but can include:

• Tears in the colon or rectum wall
• Bleeding
• Reaction to the sedative

There are fewer risks to sigmoidoscopy than with a colonoscopy. Tears and bleeding can happen in the colon, but they are even less common than with a colonoscopy.

In a virtual colonoscopy, risks include:

• Exposure to a small dose of radiation from the scan
• Rarely, a tear in the colon or rectum can happen when it is inflated with air

Seek medical care immediately if you have severe abdominal pain, blood in your stool or bleeding from your anus, dizziness, or weakness.

What do the results mean?

If your fecal occult blood test or stool DNA test had abnormal results, it doesn't necessarily mean you have cancer. But your provider will probably order more tests, such as a colonoscopy, to help make a diagnosis.

Abnormal results for the other types of screening tests may include the following:

Colonoscopy

• Colorectal polyps or abnormal tissue were found and removed.
• Samples were sent to a lab for testing.

Most polyps aren't cancerous but can turn into cancer if not removed. Depending on the size and number of polyps, your provider may recommend more frequent colonoscopies.

Sigmoidoscopy

• Colorectal polyps or abnormal tissue were found. They may or may not be removed depending on their location.
• Whether or not your polyps were removed, you will probably need a colonoscopy so your provider can view your entire colon and rectum.

Virtual colonoscopy

• Colorectal polyps or abnormal tissue were seen on the CT scan.
• You may need a traditional colonoscopy so your provider can get a tissue sample. Sometimes this procedure can be done on the same day as your virtual colonoscopy.

If you have questions about your results, talk to your provider.

Is there anything else I need to know about colorectal cancer screening?

Each type of screening test has advantages and disadvantages. You and your provider should discuss the benefits and risks of each option. The following may help guide your decision: