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 different 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 inserted into the rectum or with special imaging (x-ray) tests. Polyps found before they become cancerous 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 that cancer may be present. These tests are less invasive and easier to have done, but they are less likely to detect polyps.

These tests as well as others can also 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 is inserted through the rectum and into the lower part of the colon. Images from the scope are viewed on a display monitor.

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

Before the test: Your colon and rectum must be empty and clean so your doctor can view the lining of the sigmoid colon and rectum. Your doctor will give you 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 exam. You may also be asked to use enemas or to use strong laxatives to clean out your colon before the exam. 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 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 less uncomfortable, but you will need some time to recover from it and you’ll need someone with you to take you home after the test.

You will probably be asked to lie on a table on your left side with your knees positioned near your chest. Your doctor may examine the rectum before inserting the sigmoidoscope by inserting a gloved, lubricated finger into the rectum. The sigmoidoscope is lubricated to make it easier to insert into the rectum. The scope may feel cold. The sigmoidoscope may stretch the wall of the colon, which may cause bowel spasms or lower abdominal pain. Air will be placed into the sigmoid 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 abdomen. To ease discomfort and the urge to have a bowel movement, it helps to breathe deeply and slowly through your mouth. You will feel better after the test once the air leaves your colon.

If a small polyp is found during the test your doctor may remove it with a small instrument passed through the scope. The polyp will be sent to a lab to be looked at by a pathologist. If a pre-cancerous polyp (an adenoma) or colorectal cancer is found during the test, you will 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. Significant 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 is basically a longer version of a sigmoidoscope. It is inserted 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, as 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 2 to 4 quarts of a salty liquid laxative the evening before and the morning of the procedure. This leads to spending much of the night before and the morning of the procedure in the bathroom.

Your doctor will give you specific instructions. It is important to read these carefully a few days ahead of time, since you may need to shop for special supplies and get laxatives from a pharmacy. If you are not sure about any of the instructions, call the doctor’s office and go over them step by step with the nurse.

You might be given other instructions as well. Your doctor may tell you to stop eating food and drink only clear liquids (water, apple or white grape juice, and any gelatin except red or purple) for at least a day before the exam. Plain tea or coffee with sugar is usually okay, but no milk or creamer is allowed. Clear broth, ginger ale, and most soft drinks or sports drinks are usually allowed unless they have red or purple food colorings, which could be mistaken for blood in the colon.

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 will need to arrange for someone you know to take you home from the test (not just a cab).

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 colonoscopy begins, you will be given a sedating medicine (into a vein) to make you feel comfortable and sleepy during the procedure. For most people, this medicine leads to them being unaware of what is going on and unable to remember the procedure afterward. You will wake up after the test is over, but might not be fully awake until later in the day.

During the procedure, you will be asked to lie on your side with your knees flexed and 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 inserting the colonoscope. The colonoscope is lubricated so it can be easily inserted 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 are awake, you may feel an urge to have a bowel movement when the colonoscope is inserted or pushed further up the colon. To ease any discomfort it may help to breathe deeply and slowly through your mouth. The doctor injects 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.

The doctor will look at the inner walls of the colon as he or she slowly withdraws the colonoscope. If a small polyp is found, the doctor may remove it. Some small polyps may eventually become cancerous. For this reason, they are usually removed. This is usually done by passing a wire loop through the colonoscope to cut the polyp from the wall of the colon with an electrical current. The polyp can then be sent to a lab to be checked under a microscope 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. For this procedure, a small piece of tissue is taken out through the colonoscope. The tissue is looked at under a microscope to determine if it is a 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 may 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 is passed out.

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

If a polyp is removed or a biopsy is done during the colonoscopy, you may notice some blood in your stool for a day or 2 after the test. Significant bleeding is uncommon, but in rare cases, there is serious bleeding that requires treatment or can even be life-threatening.

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

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

Double-contrast barium enema

The double-contrast barium enema (DCBE) is also called an air-contrast barium enema or a barium enema with air contrast. It may also be referred to as a lower GI series. It is basically a type of x-ray test. Barium sulfate, which is a chalky liquid, and air are used to outline the inner part of the colon and rectum to look for 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: As with colonoscopy, it is very important that the colon and rectum are empty and clean so your doctor can see them during the test. Your doctor will give you specific instructions on preparing for the test. Be sure to follow them. 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 will probably be asked to follow a clear liquid diet for a day or 2 before the procedure. 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 procedure.

During the test: The procedure takes about 30 to 45 minutes, and it does not require sedation. For this test, you lie on a table on your side in an x-ray room. A small, flexible tube is inserted into the rectum, and barium sulfate is pumped in to partially 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 to make it expand. This may 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 are then taken, allowing the doctor to look for polyps or cancers. You may be asked to change positions 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 will 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 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 appear grey or white until the barium leaves the body. There is a very small risk that inflating the colon with air could injure or puncture the colon, 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 is an x-ray test that produces 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 does not require sedation. But even though this test is not invasive like colonoscopy, it still requires the same type of bowel preparation and uses a tube placed in the rectum (similar to the tube used for barium enema) 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 is important that the colon and rectum are emptied before this test to provide the best images, so the preparation for this test is similar to that for a colonoscopy. You will probably be told to follow a clear liquid diet for a day or 2 before the test. There are a number of ways to clean the colon before the procedure. Often, the evening before the procedure, you drink 2 to 4 quarts of a salty liquid laxative solution. This often results in spending much of the night before the procedure in the bathroom. The morning of the procedure, sometimes more liquid needs to be drunk or enemas need to be used to make sure the bowels are empty.

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

Possible side effects and complications: There are usually very few side effects after CT colonography. You may feel bloated or have cramps because of the air in the colon, but this should go away once the air passes from the body. There is a very small risk that inflating the colon with air could injure or puncture the colon, 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 for signs of cancer. Most people find these tests to be easier because they are not invasive and can often be done at home. But these tests aren't as good as the ones described that find polyps. A positive result on one of these screening tests will probably require a more invasive test such as colonoscopy.

Guaiac-based fecal occult blood test

One way to find for colorectal cancer is to look for blood that can't be seen with the naked eye (occult blood) in feces (stool). The idea behind this test is that blood vessels at the surface of larger colorectal polyps or cancers are often fragile and easily damaged by the passage of feces. The damaged vessels usually release a small amount of blood into the feces, but only rarely is there enough bleeding for blood to be visible in the stool.

The guaiac-based fecal occult blood test (gFOBT) detects blood in the stool through a chemical reaction. This test cannot 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 cancers and polyps can cause blood in the stool, other causes of bleeding can occur, 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 is more likely to find colorectal cancer if it is present. The American Cancer Society recommends the more modern version of this test for screening, called “highly-sensitive.”

This screening 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 is not sufficient for screening (it only checks one stool sample). Also, unlike some other tests (like colonoscopy), this one must be repeated every year.

People having this test will receive a kit with instructions from their doctor's office or clinic. The kit will explain how to take a stool or feces sample at home (usually specimens from 3 consecutive bowel movements that are smeared onto small squares of paper). The kit should then be 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 test result, so your doctor may suggest that you avoid the following before this test:

  • Nonsteroidal 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.
  • 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 when 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 give it to their doctor because they worry that something they ate may interfere with the test. For this reason, many doctors tell their patients it isn't essential to follow any restrictions in their diet. The most important thing is to get the test done. People should try to avoid taking aspirin or related drugs 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.

Collecting the samples: Have all of your supplies ready and in one place. Supplies will 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 specimen. The instructions below can be used as a guide, but your kit instructions might be a little different. Always follow the instructions on your kit.

  • You will need to collect a sample from your bowel movement. You can place a sheet of plastic wrap or paper loosely across the toilet bowl to catch the stool or you can use a dry container to collect the stool. Do not let the stool specimen mix with urine. After you obtain a sample, you can flush the remaining stool down the toilet.
  • Use a wooden applicator or a brush to smear a thin film of the stool sample onto one of the slots in the test card or slide.
  • Next, collect a specimen from a different area of the same stool and smear a thin film of the sample onto the other slot in the test card or slide.
  • Close the slots and put your name and the date on the test kit. Store the kit overnight in a paper envelope to allow it time to dry.
  • Repeat the test on your next 2 bowel movements if instructed. Most tests require collecting more than one sample from different bowel movements. This improves the accuracy of the test because many cancers don't bleed all of the time, and blood may not be present in all stool samples.
  • Place the test kit in the mailing pouch provided and return it to your doctor or lab as soon as possible (but within 14 days of taking the first sample).

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

Fecal immunochemical test

The fecal immunochemical test (FIT), also called an immunochemical fecal occult blood test (iFOBT), tests for occult (hidden) blood in the stool in a different way than a guaiac-based test. 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. Versions that the American Cancer Society recommends for screening, called “highly-sensitive,” have been around for at least 10 years.

The FIT is done essentially the same way as the FOBT, but some people may find it easier to use because there are no drug or dietary restrictions (vitamins or foods do not affect the FIT) and sample collection may take less effort. This test is also less likely to react to bleeding from parts of the upper digestive tract, such as the stomach.

Like the FOBT, the FIT may not detect a tumor that is not bleeding, so multiple stool samples should be tested. And if the results are positive for hidden blood, a colonoscopy is required to investigate further. To be beneficial the test must be repeated every year.

Collecting the samples: Have all of your supplies ready and in one place. Supplies will include a test kit, test cards, long brushes, waste bags, and a mailing envelope. The kit will give you detailed instructions on how to collect the specimen. The instructions below can be used as a guide, but the instructions on your kit might be a little different. Always follow the instructions on your kit.

  • Flush the toilet before your bowel movement. After you go, place used toilet paper in the waste bag from the kit, not in the toilet.
  • Brush the surface of the stool with one of the brushes, then dip the brush in the toilet water. Dab the end of the brush onto one of the slots in the test card or slide.
  • Close the slot and put your name and the date on the test kit.
  • Repeat the test on your next bowel movement if instructed. Most tests require collecting more than one sample from different bowel movements. This improves the accuracy of the test because many cancers don't bleed all of the time, and blood may not be present in all stool samples.
  • Place the test kit in the mailing envelope provided and return it to your doctor or lab as soon as possible (but within 14 days of taking the first sample).

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 contain DNA mutations (changes) in certain genes. Cells from colorectal cancers or polyps with these mutations are often shed 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 will receive a kit in the mail to collect your stool samples. It will contain 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 samples. The instructions below can be used as a guide.

  • Place the bracket under the toilet seat and then put the toilet seat down.
  • Remove the lid from the sample container and place it in the bracket (in the toilet).
  • Sit on the toilet and try to have a bowel movement into the container. Try to keep urine from going in the container.
  • When your bowel movement is complete, stand up and remove the container from the toilet (you can discard the bracket). Do not put toilet paper in the container.
  • Remove the cap from the tube that was included in the kit and pull the probe (like a stick) from the tube.
  • Scrape the stool in the container with the probe so that stool gets on the end.
  • Put the probe back in the tube and screw the cap shut.
  • Open the bottle of liquid preservative and pour all of the liquid over the stool in the container.
  • Put the lid on the sample container and screw it down tight.
  • Label the samples and ship them according to the instructions in the kit. The samples should shipped within a day of collection.

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 preparation

    Sedation usually not used

    Does not require a specialist

    Done every 5 years

    Views 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 view entire colon

    Can biopsy and remove polyps

    Done every 10 years

    Can diagnose other diseases

    Can miss small polyps

    Full bowel preparation needed

    More expensive on a one-time basis than other forms of testing

    Sedation of some kind is usually needed

    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 view entire colon

    Relatively safe

    Done every 5 years

    No sedation needed

    Can miss small polyps

    Full bowel preparation needed

    Some false positive test results

    Cannot remove polyps during testing

    Colonoscopy will be needed if abnormal

    CT colonography (virtual colonoscopy)

    Fairly quick and safe

    Can usually view entire colon

    Done every 5 years

    No sedation needed

    Can miss small polyps

    Full bowel preparation needed

    Some false positive test results

    Cannot 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 preparation

    Sampling done at home

    Inexpensive

    May miss many polyps and some cancers

    May produce false-positive test results

    May have pre-test dietary limitations

    Should be done every year

    Colonoscopy will be needed if abnormal

    Fecal immunochemical test (FIT)

    No direct risk to the colon

    No bowel preparation

    No pre-test dietary restrictions

    Sampling done at home

    Fairly inexpensive

    May miss many polyps and some cancers

    May produce false-positive test results

    Should be done every year

    Colonoscopy will be needed if abnormal

    Stool DNA test

    No direct risk to the colon

    No bowel preparation

    No pre-test dietary restrictions

    Sampling done at home

    May miss many polyps and some cancers

    May produce false-positive test results

    Should be done every 3 years

    Colonoscopy will be needed if abnormal


Last Medical Review: 10/15/2014
Last Revised: 10/29/2014