Colorectal Cancer Prevention and Early Detection

+ -Text Size

TOPICS

Colorectal cancer screening tests

Screening is the process of looking for cancer in people who have no symptoms of the disease. Several tests can be used to screen for colorectal cancers. These tests can be divided into:

  • Tests that can find both colorectal polyps and cancer: These tests look at the structure of the colon itself to find any abnormal areas. This is done either with a scope put into the rectum or with special imaging (x-ray) tests. Polyps found during these tests can be removed before they become cancerous, 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 tests check the stool (feces) for signs of cancer. These tests are less invasive and easier to have done, but they are less likely to detect polyps.

These tests as well as others also can be used when people have symptoms of colorectal cancer and other digestive diseases.

Tests that can find both colorectal polyps and cancer

Flexible sigmoidoscopy

During this test, the doctor looks at part of the colon and rectum with a sigmoidoscope – a flexible, lighted tube about the thickness of a finger with a small video camera on the end. It’s put in through the rectum and moved into the lower part of the colon. Images from the scope are seen on a display monitor.

Using the sigmoidoscope, your doctor can look at the inside of the rectum and part of the colon to detect (and possibly remove) any abnormality. The sigmoidoscope is only 60 centimeters (about 2 feet) long, so the doctor is able to see the entire rectum but less than half of the colon with this procedure.

Before the test: Be sure your doctor knows about any medicines you are taking. You might need to change how you take them before the test. Your colon and rectum must be empty and clean so your doctor can see the lining of the sigmoid colon and rectum. You will get specific instructions to follow to clean them out. You may be asked to follow a special diet (such as drinking only clear liquids) for a day before the test. You may also be asked to use enemas or to use strong laxatives to clean out your colon before the test. Be sure to tell your doctor about any medicines you are taking, as you might need to change how you take them before the test.

During the test: A sigmoidoscopy usually takes about 10 to 20 minutes. Most people don’t need to be sedated for this test, but this might be an option you can discuss with your doctor. Sedation may make the test less uncomfortable, but you’ll need some time to recover from it and you’ll need someone with you to take you home after the test.

You’ll probably be asked to lie on a table on your left side with your knees pulled up near your chest. Before the test, your doctor may put a gloved, lubricated finger into your rectum to examine it. For the test itself, the sigmoidoscope is first lubricated to make it easier to insert into the rectum. The scope may feel cold as it’s put in. Air will be pumped into the colon through the sigmoidoscope so the doctor can see the walls of the colon better.

During the procedure, you might feel pressure and slight cramping in your lower belly. To ease discomfort and the urge to have a bowel movement, it helps to breathe deeply and slowly through your mouth. You’ll feel better after the test once the air leaves your colon.

If a small polyp is found during the test, the doctor may remove it with a small instrument passed through the scope. The polyp will be sent to a lab to be looked at. If a pre-cancerous polyp (an adenoma) or colorectal cancer is found, you’ll need to have a colonoscopy later to look for polyps or cancer in the rest of the colon.

Possible complications and side effects: This test may be uncomfortable because of the air put into the colon, but it should not be painful. Be sure to let your doctor know if you feel pain during the procedure. You might see a small amount of blood in your first bowel movement after the test. More serious bleeding and puncture of the colon are possible complications, but they are very uncommon.

Colonoscopy

For this test, the doctor looks at the entire length of the colon and rectum with a colonoscope, a thin, flexible, lighted tube with a small video camera on the end. It’s basically a longer version of a sigmoidoscope. It’s put in through the anus and into the rectum and colon. Special instruments can be passed through the colonoscope to biopsy (sample) or remove any suspicious-looking areas such as polyps, if needed.

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

Before the test: Be sure your doctor knows about any medicines you are taking. You might need to change how you take them before the test. The colon and rectum must be empty and clean so your doctor can see their inner linings during the test. This can be done many ways, but the most common involves drinking large amounts of a liquid laxative the evening before and the morning of the procedure. This leads to spending a lot of time in the bathroom.

Your doctor will give you specific instructions. It’s important to read these carefully a few days ahead of time, since you may need to follow a special diet for at least a day before the test and to shop for supplies and laxatives. If you’re not sure about any of the instructions, call the doctor’s office and go over them with the nurse.

You will probably also be told not to eat or drink anything after midnight the night before your test. If you normally take prescription medicines in the mornings, talk with your doctor or nurse about how to manage them for the day.

Because a sedative is used during the test, you’ll need to arrange for someone you know to take you home from the test (not just a cab or Uber).

During the test: The test itself usually takes about 30 minutes, but it may take longer if a polyp is found and removed. Before it starts, you’ll be given a sedating medicine (into a vein) to make you feel relaxed and sleepy during the procedure. For most people, this medicine makes them unaware of what’s going on and unable to remember the procedure afterward. You’ll wake up after the test is over, but might not be fully awake until later in the day.

During the test, you’ll be asked to lie on your side with your knees pulled up. A drape will cover you. Your blood pressure, heart rate, and breathing rate will be monitored during and after the test.

Your doctor might insert a gloved finger into the rectum to examine it before putting in the colonoscope. The colonoscope is lubricated so it can be inserted easily into the rectum. Once in the rectum, the colonoscope is passed all the way to the beginning of the colon, called the cecum.

If you’re awake, you may feel an urge to have a bowel movement when the colonoscope is inserted or pushed further up the colon. The doctor also puts air into the colon through the colonoscope to make it easier to see the lining of the colon and use the instruments to perform the test. To ease any discomfort, it may help to breathe deeply and slowly through your mouth.

The doctor will look at the inner walls of the colon as he or she slowly removes the colonoscope. If a small polyp is found, it may be removed. This is because some small polyps may become cancer over time. Removing the polyp is usually done by passing a wire loop through the colonoscope to cut the polyp from the wall of the colon with an electric current. The polyp is then sent to a lab to be checked to see if it has any areas that have changed into cancer.

If your doctor sees a larger polyp or tumor or anything else abnormal, a biopsy may be done. A small piece of tissue is taken out through the colonoscope. The tissue is checked in the lab to see if it’s cancer, a benign (non-cancerous) growth, or a result of inflammation.

Possible side effects and complications: The bowel preparation before the test is unpleasant. The test itself might be uncomfortable, but the sedative usually helps with this, and most people feel normal once the effects of the sedative wear off. Because air is pumped into the colon during the test, people sometimes feel bloated, have gas pains, or have cramping for a while after the test until the air passes out.

Some people may have low blood pressure or changes in heart rhythm due to the sedation during the test, but these are rarely serious.

If a polyp is removed or a biopsy is done during the colonoscopy, you might notice some blood in your stool for a day or 2 after the test. Serious bleeding is uncommon, but in rare cases, bleeding might need to be treated or can even be life-threatening.

Colonoscopy is a safe procedure, but in rare cases the colonoscope can puncture the wall of the colon or rectum. This is called a perforation. Symptoms can include severe abdominal (belly) pain, nausea, and vomiting. This can be a major (or even life-threatening) complication, because it can lead to a serious abdominal (belly) infection. The hole may need to be repaired with surgery. Ask your doctor about the risk of this complication.

You can read more about colonoscopy and sigmoidoscopy in Frequently Asked Questions About Colonoscopy and Sigmoidoscopy.

Double-contrast barium enema (DCBE)

This test is also called an air-contrast barium enema or a barium enema with air contrast. It may also be called a lower GI series. It’s basically a type of x-ray test. Barium sulfate, which is a chalky liquid, and air are put into the colon and rectum to outline the inner lining. This can show abnormal areas on x-rays. If suspicious areas are seen on this test, a colonoscopy will be needed to explore them further.

Before the test: It’s very important that the colon and rectum are empty and clean so they can be seen during the test. You’ll be given specific instructions on how to prepare for the test. For example, you may be asked to clean your bowel the night before with laxatives and/or take enemas the morning of the exam. You’ll probably be asked to follow a clear liquid diet for at least a day before the test. You may also be told to avoid eating or drinking dairy products the day before the test, and to not eat or drink anything after midnight on the night before the test.

During the test: The test takes about 30 to 45 minutes, and sedation isn’t needed. You lie on a table on your side in an x-ray room. A small, flexible tube is put into your rectum, and barium sulfate is pumped in to partially fill and open up the colon and rectum. You are then turned on the x-ray table so the barium moves throughout the colon and rectum. Then air is pumped into the colon and rectum through the same tube to expand them. This might cause some cramping and discomfort, and you may feel the urge to have a bowel movement.

X-ray pictures of the lining of your colon and rectum are then taken to look for polyps or cancers. You may be asked to change positions to help move the barium and so that different views of the colon and rectum can be seen on the x-rays.

If polyps or other suspicious areas are seen on this test, you’ll probably need a colonoscopy to remove them or to explore them fully.

Possible side effects and complications: You may have bloating or cramping after the test, and will probably 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. There’s a very small risk that inflating the colon with air could injure or puncture it, but this risk is thought to be much less than with colonoscopy. Like other x-ray tests, this test also exposes you to a small amount of radiation.

CT colonography (virtual colonoscopy)

This test is an advanced type of computed tomography (CT or CAT) scan of the colon and rectum. A CT scan uses x-rays to make detailed cross-sectional images of your body. Instead of taking one picture, like a regular x-ray, a 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.

For CT colonography, special computer programs create both 2-dimensional x-ray pictures and a 3-dimensional “fly-through” view of the inside of the colon and rectum, which lets the doctor look for polyps or cancer.

This test may be especially useful for some people who can’t have or don’t want to have more invasive tests such as colonoscopy. It can be done fairly quickly, and sedation isn’t needed. But even though this test is not invasive like colonoscopy, the same type of bowel prep is needed. Also, a small, flexible tube is put in the rectum to fill the colon with air. Another possible drawback is that if polyps or other suspicious areas are seen on this test, a colonoscopy will still probably be needed to remove them or to explore them fully.

Before the test: It’s important that the colon and rectum are emptied before this test to get the best images. You’ll probably be told to follow a clear liquid diet for at least a day before the test. There are a number of ways to clean out the colon before the test. Often, the evening before the procedure, you drink large amounts of a liquid laxative solution. This often results in spending a lot of time in the bathroom. The morning of the test, sometimes more laxatives or enemas may be needed to make sure the bowels are empty.

During the test: This test is done in a special room with a CT scanner. It takes about 10 minutes. You may be asked to drink a contrast solution before the test to help “tag” any stool left in the colon or rectum, which helps the doctor when looking at the test images. You’ll be asked to lie on a thin table that’s part of the CT scanner, and will have a small, flexible tube put into your rectum. Air is pumped through the tube into the colon and rectum to expand them to provide better images. The table then slides into the CT scanner, and you’ll be asked to hold your breath while the scan is done. You’ll likely have 2 scans: one while you’re lying on your back and one while you’re on your stomach. Each scan usually takes only about 10 to 15 seconds.

Possible side effects and complications: There are usually few side effects after this test. You may feel bloated or have cramps because of the air in the colon and rectum, but this should go away once the air passes from the body. There’s a very small risk that inflating the colon with air could injure or puncture it, but this risk is thought to be much less than with colonoscopy. Like other types of CT scans, this test also exposes you to a small amount of radiation.

Tests that mainly find colorectal cancer

These tests look at the stool (feces) for signs of cancer. Most people find these tests easier to have than tests like colonoscopy, and these tests can often be done at home. But these tests aren’t as good at finding polyps as tests like colonoscopy. And if the result from one of these stool tests is positive (abnormal), you’ll probably still need a colonoscopy to see if you have cancer.

Guaiac-based fecal occult blood test (gFOBT)

One way to test for colorectal cancer is to look for occult (hidden) blood in stool. The idea behind this test is that blood vessels in larger colorectal polyps or cancers are often fragile and easily damaged by the passage of feces. The damaged vessels usually bleed into the feces, but only rarely is there enough bleeding for blood to be seen in the stool.

The guaiac-based fecal occult blood test (gFOBT) detects blood in the stool through a chemical reaction. This test can’t tell if the blood is from the colon or from other parts of the digestive tract (such as the stomach). If this test is positive, a colonoscopy will be needed to find the reason for the bleeding. Although blood in the stool can be from cancers or polyps, it can also have other causes, such as ulcers, hemorrhoids, diverticulosis (tiny pouches that form at weak spots in the colon wall), or inflammatory bowel disease (colitis).

Over time, this test has improved so that it’s now more likely to find colorectal cancer. The American Cancer Society recommends the more modern, “highly sensitive” versions of this test for screening.

This test is done with a kit that you can use in the privacy of your own home that allows you to check more than one stool sample. A FOBT done during a digital rectal exam in the doctor’s office (which only checks one stool sample) is not sufficient for screening. Also, unlike some other tests (like colonoscopy), this test must be done every year.

People having this test will get a kit with instructions from their doctor’s office or clinic. The kit will explain how to take stool samples at home (usually samples from 3 consecutive bowel movements are smeared onto small squares of paper). The kit is then returned to the doctor’s office or medical lab (usually within 2 weeks) for testing.

Before the test: Some foods or drugs can affect the results, so you may be instructed to avoid the following before this test:

  • Non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen (Advil), naproxen (Aleve), or aspirin (more than 1 adult aspirin per day), for 7 days before testing. (They can cause bleeding, which can lead to a false-positive result.) Acetaminophen (Tylenol) can be taken as needed. Note: People should try to avoid taking NSAIDs for minor aches. But if you take these medicines daily for heart problems or other conditions, don’t stop them for this test without talking to your doctor first.
  • Vitamin C in excess of 250 mg daily from either supplements or citrus fruits and juices for 3 days before testing. (This can affect the chemicals in the test and make the result negative, even if blood is present.)
  • Red meats (beef, lamb, or liver) for 3 days before testing. (Components of blood in the meat may cause a positive test result.)

Some people who are given the test never do it or don’t return it because they worry that something they ate may affect the test. For this reason, many doctors tell their patients it’s not critical that they follow the diet restrictions. The most important thing is to get the test done.

Collecting the samples: Have all of your supplies ready and in one place. Supplies typically include a test kit, test cards, either a brush or wooden applicator, and a mailing envelope. The kit will give you detailed instructions on how to collect the stool samples. Be sure to follow the instructions that come with your kit, as different kits might have different instructions. If you have any questions about how to use your kit, contact your doctor’s office or clinic. Once you have collected the samples, return them as instructed in the kit.

If this test finds blood, a colonoscopy will be needed to look for the source. It’s not enough to simply repeat the gFOBT or follow up with other types of tests.

Fecal immunochemical test (FIT)

The fecal immunochemical test (FIT) is also called an immunochemical fecal occult blood test (iFOBT). It tests for occult (hidden) blood in the stool in a different way than a guaiac-based FOBT. This test reacts to part of the human hemoglobin protein, which is found in red blood cells.

Early versions of this test were not as good at finding colorectal cancers. Highly sensitive versions, which the American Cancer Society recommends for screening, have been around for at least 10 years.

The FIT is done much like the gFOBT, in that small amounts of stool are collected on cards (or in tubes). Some people may find this test easier because there are no drug or dietary restrictions (vitamins and foods do not affect the FIT), and collecting the sample may be easier. This test is also less likely to react to bleeding from other parts of digestive tract, such as the stomach.

Like the gFOBT, the FIT may not detect a tumor that’s not bleeding, so multiple stool samples should be tested. And if the results are positive for hidden blood, a colonoscopy will be needed to investigate further. This test must be done every year.

Collecting the samples: Have all of your supplies ready and in one place. Supplies typically include a test kit, test cards or tubes, long brushes or other collecting devices, waste bags, and a mailing envelope. The kit will give you detailed instructions on how to collect the samples. Be sure to follow the instructions that come with your kit, as different kits might have different instructions. If you have any questions about how to use your kit, contact your doctor’s office or clinic. Once you have collected the samples, return them as instructed in the kit.

Stool DNA test

A stool DNA test looks for certain abnormal sections of DNA (genetic material) from cancer or polyp cells. Colorectal cancer cells often have DNA mutations (changes) in certain genes. Cells from colorectal cancers or polyps with these mutations often get into the stool, where tests may be able to detect them. Cologuard®, the test currently available, also tests for blood in the stool.

Collecting the samples: You’ll get a kit in the mail to use to collect your entire stool sample. The kit will have a sample container, a bracket for holding the container in the toilet, a bottle of liquid preservative, a tube, labels, and a shipping box. The kit contains detailed instructions on how to collect the sample. Be sure to follow the instructions that come with your kit. If you have any questions about how to use your kit, contact your doctor’s office or clinic. Once you have collected the sample, return it as instructed in the kit.

This test should be done every 3 years. If the test is positive (if it finds DNA changes or blood), a colonoscopy will be needed.

What are some of the pros and cons of these screening tests?

    Test

    Pros

    Cons

    Flexible sigmoidoscopy

    Fairly quick and safe

    Usually doesn’t require full bowel prep

    Sedation usually not used

    Does not require a specialist

    Done every 5 years

    Looks at only about a third of the colon

    Can miss small polyps

    Can’t remove all polyps

    May be some discomfort

    Very small risk of bleeding, infection, or bowel tear

    Colonoscopy will be needed if abnormal

    Colonoscopy

    Can usually look at the entire colon

    Can biopsy and remove polyps

    Done every 10 years

    Can help find some other diseases

    Can miss small polyps

    Full bowel prep needed

    Costs more on a one-time basis than other forms of testing

    Sedation is usually needed

    You will need someone to drive you home

    You may miss a day of work

    Small risk of bleeding, bowel tears, or infection

    Double-contrast barium enema (DCBE)

    Can usually see the entire colon

    Relatively safe

    Done every 5 years

    No sedation needed

    Can miss small polyps

    Full bowel prep needed

    Some false positive test results

    Can’t remove polyps during testing

    Colonoscopy will be needed if abnormal

    CT colonography (virtual colonoscopy)

    Fairly quick and safe

    Can usually see the entire colon

    Done every 5 years

    No sedation needed

    Can miss small polyps

    Full bowel prep needed

    Some false positive test results

    Can’t remove polyps during testing

    Colonoscopy will be needed if abnormal

    Still fairly new – may be insurance issues

    Guaiac-based fecal occult blood test (gFOBT)

    No direct risk to the colon

    No bowel prep

    Sampling done at home

    Inexpensive

    Can miss many polyps and some cancers

    Can produce false-positive test results

    Pre-test diet changes are needed

    Needs to be done every year

    Colonoscopy will be needed if abnormal

    Fecal immunochemical test (FIT)

    No direct risk to the colon

    No bowel prep

    No pre-test diet changes

    Sampling done at home

    Fairly inexpensive

    Can miss many polyps and some cancers

    Can produce false-positive test results

    Needs to be done every year

    Colonoscopy will be needed if abnormal

    Stool DNA test

    No direct risk to the colon

    No bowel prep

    No pre-test diet changes

    Sampling done at home

    Can miss many polyps and some cancers

    Can produce false-positive test results

    Should be done every 3 years

    Colonoscopy will be needed if abnormal

    Still fairly new – may be insurance issues


Last Medical Review: 01/27/2016
Last Revised: 06/24/2016