URL of this page: https://medlineplus.gov/lab-tests/colorectal-cancer-screening-tests/

Colorectal Cancer Screening Tests

What are colorectal cancer screening tests?

Colorectal cancer screening tests check for signs of colorectal cancer. 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 is a leading cause of cancer deaths in the United States. Screening can help find colorectal cancer early, when treatment is most effective. Colorectal cancer screening can sometimes prevent cancer from even developing. That's because some types of screening tests let a health care provider find and remove abnormal growths, known as colorectal polyps. Most of these polyps are benign (not cancerous) but do have a risk of becoming cancerous if not removed.

Other names: colon cancer screening

What are they used for?

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

Why do I need a colorectal cancer screening test?

The National Cancer Institute and other expert medical groups recommend people get regular screenings for colorectal cancer, starting at age 50. The American Cancer Society recommends that people begin screening at age 45. You should talk with your health care provider about when you should start and about the different types of screening tests.

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

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 are procedures that allow a provider to look inside the colon and rectum. They are done either using a thin tube with a camera attached or with a special imaging device. Types of visual exams include:

Colonoscopy. This test allows a provider to view your entire colon and rectum. It is often done in an outpatient department of a hospital or medical center. Before the test, you will need to empty out your colon (large bowel) in a procedure called bowel prep. During the test:

  • You will lie on an exam table.
  • You will be given medicine called a sedative to help you relax. It also prevents you from feeling pain during the procedure. You may be awake for the test, but you 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.
  • Your provider will look for colorectal polyps or other abnormal areas.
  • 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.

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

Sigmoidoscopy. This test allows your provider to look at the lower part of the 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 the rectum and up into the lower part of the colon.
  • Air will be pumped through the sigmoidoscope to make the 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 is a type of x-ray that uses a CT scan (computed tomography) to take detailed, 3-dimensional pictures of the entire colon and rectum. It is usually done in a radiology department of a hospital or medical center. 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 the rectum.
  • Air will be pumped through the tube to make the colon bigger and easier to see.
  • The table will slide into the CT machine.
  • A series of images will be taken.

Stool tests look at stool samples for signs of cancer. For these tests, you take a stool sample at home and send it to a lab. Types of stool tests:

Fecal occult blood tests. These tests look for hidden (known as occult) blood in the stool. Blood in the stool may be a sign of polyps, cancer, or other conditions. Your health care 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 samples from two or three separate bowel movements.
  • 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 surface of the stool.
  • Brush the sample onto a test card.
  • Label and seal all your samples as directed.
  • Mail the samples to your health care 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, also included in your kit.
  • Label and seal all your samples as directed.
  • Mail the samples to your health care provider or lab.

Stool DNA test. This test checks for genetic changes in the 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.
  • Drinking a strong liquid laxative and/or using an enema on the evening before your test.
  • The laxative or enema will help you empty your bowels. You should prepare to spend a lot of time in the 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 full picture of your colon and rectum. Polyps and other abnormal areas may not be seen.

    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.
    • Use an enema to empty your bowels about one hour before the procedure. A second enema is sometimes needed.

    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
    • More than 250 mg of vitamin C daily from supplements, fruit juices, or fruit
    • Red meat, such as beef, lamb, or pork

    Your health care 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 in the colon and bleeding can happen, 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.

    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 will probably 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 health care provider.

    Is there anything else I need to know about a 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.

    Colonoscopy
    Advantages
    • Looks at the entire colon
    • Can remove polyps and test for cancer
    • May help find other diseases
    • Needed only every 10 years (if no polyps were found in previous tests)
    Disadvantages
    • Small risk of tears and bleeding
    • Bowel prep needed
    • Sedatives are needed for the procedure
    • Takes at least one day for bowel prep and recovery
    Sigmoidoscopy
    Advantages
    • Usually doesn't require bowel prep
    • Sedatives are not usually needed
    • Needed every five years (if no polyps were found in previous tests)
    Disadvantages
    • Only looks at a third of the colon
    • May miss small polyps
    • Can't remove all polyps
    • Very small risk of tears or bleeding
    • Not widely used as a screening test
    • Colonoscopy will be needed if results are abnormal
    Virtual Colonoscopy
    Advantages
    • Looks at the entire colon
    • Sedatives not needed
    • Needed every five years (if no polyps were found in previous tests)
    Disadvantages
    • Bowel prep needed
    • May miss small polyps
    • Exposure to a small amount of radiation
    • Traditional colonoscopy will be needed if results are abnormal
    • Fairly new test; may not be covered by insurance
    Fecal immunochemical test (FIT)
    Advantages
    • No risk to colon
    • No bowel prep
    • Sample can be collected at home
    Disadvantages
    • Can have false positives
    • Cannot detect precancerous changes (cells that are at risk for turning into cancer)
    • May miss some signs of polyps and/or cancer
    • Colonoscopy will be needed if results are abnormal
    • Should be done every year
    Guaiac smear test (gFOBT)
    Advantages
    • No risk to colon
    • No bowel prep
    • Sample can be collected at home
    Disadvantages
    • Can have false positives
    • Cannot detect precancerous changes
    • May miss some signs of polyps and/or cancer
    • Dietary restrictions required before testing
    • Colonoscopy will be needed if results are abnormal
    • Should be done every year
    Stool DNA
    Advantages
    • No risk to colon
    • No bowel prep
    • Sample can be collected at home
    Disadvantages
    • Can have false positives
    • Cannot detect precancerous changes
    • May miss some cancers
    • Colonoscopy will be needed if results are abnormal
    • Should be done every three years
    • Fairly new test; may not be covered by insurance


    References

    1. American Cancer Society [Internet]. Atlanta: American Cancer Society Inc.; c2020. American Cancer Society Guideline for Colorectal Cancer Screening; [updated 2020 Nov 17; cited 2020 Dec 17]; [about 4 screens]. Available from: https://www.cancer.org/cancer/colon-rectal-cancer/detection-diagnosis-staging/acs-recommendations.html
    2. American Cancer Society [Internet]. Atlanta: American Cancer Society Inc.; c2020. Can Colorectal Polyps and Cancer Be Found Early?; [updated 2020 Jun 29; cited 2020 Dec 17]; [about 3 screens]. Available from: https://www.cancer.org/cancer/colon-rectal-cancer/detection-diagnosis-staging/detection.html
    3. American Cancer Society [Internet]. Atlanta: American Cancer Society Inc.; c2020. Colorectal Cancer Screening Tests; [updated 2020 Jun 29; cited 2020 Dec 17]; [about 5 screens]. Available from: https://www.cancer.org/cancer/colon-rectal-cancer/detection-diagnosis-staging/screening-tests-used.html
    4. Cancer.net [Internet]. Alexandria (VA): American Society of Clinical Oncology; c2005–2020. Colorectal Cancer: Screening; 2019 Oct [cited 2020 Dec 17]; [about 3 screens]. Available from: https://www.cancer.net/cancer-types/colorectal-cancer/screening
    5. Cleveland Clinic [Internet]. Cleveland (OH): Cleveland Clinic; c2020. Colorectal (Colon) Cancer: Diagnosis and Tests; [cited 2020 Dec 17]; [about 4 screens]. Available from: https://my.clevelandclinic.org/health/diseases/14501-colorectal-colon-cancer/diagnosis-and-tests
    6. Cleveland Clinic [Internet]. Cleveland (OH): Cleveland Clinic; c2020. Colorectal (Colon) Cancer: Overview; [cited 2020 Dec 17]; [about 3 screens]. Available from: https://my.clevelandclinic.org/health/diseases/14501-colorectal-colon-cancer
    7. Colorectal Cancer Alliance [Internet]. Washington D.C.; Colorectal Cancer Alliance; c2019. Colonoscopy; [cited 2020 Dec 17]; [about 3 screens]. Available from: https://www.ccalliance.org/screening-prevention/screening-methods/colonoscopy
    8. Lab Tests Online [Internet]. Washington D.C.: American Association for Clinical Chemistry; c2001–2020. Colon Cancer; [updated 2020 Jun 7; cited 2020 Dec 17]; [about 2 screens]. Available from: https://labtestsonline.org/conditions/colon-cancer
    9. Lab Tests Online [Internet]. Washington D.C.: American Association for Clinical Chemistry; c2001–2020. Fecal Immunochemical Test and Fecal Occult Blood Test; [updated 2020 May 21; cited 2020 Dec 17]; [about 2 screens]. Available from: https://labtestsonline.org/tests/fecal-immunochemical-test-and-fecal-occult-blood-test
    10. Mayo Clinic [Internet]. Mayo Foundation for Medical Education and Research; c1998–2020. Flexible sigmoidoscopy: Overview; 2020 May 6 [cited 2020 Dec 17]; [about 3 screens]. Available from: https://www.mayoclinic.org/tests-procedures/flexible-sigmoidoscopy/about/pac-20394189
    11. Mayo Clinic [Internet]. Mayo Foundation for Medical Education and Research; c1998–2020. Virtual colonoscopy: Overview; 2017 Sep 23 [cited 2020 Dec 17]; [about 3 screens]. Available from: https://www.mayoclinic.org/tests-procedures/virtual-colonoscopy/about/pac-20385156
    12. National Cancer Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Colorectal Cancer Screening (PDQ) Patient Version; [updated 2019 Mar 15; cited 2020 Dec 17]; [about 4 screens]. Available from: https://www.cancer.gov/types/colorectal/patient/colorectal-screening-pdq
    13. UF Health: University of Florida Health [Internet]. Gainesville (FL): University of Florida Health; c2020. Colon cancer screening: Overview; [updated 2020 Dec 17; cited 2020 Dec 17]; [about 2 screens]. Available from: https://ufhealth.org/colon-cancer-screening
    14. UF Health: University of Florida Health [Internet]. Gainesville (FL): University of Florida Health; c2020. Colonoscopy: Overview; [updated 2020 Dec 17; cited 2020 Dec 17]; [about 2 screens]. Available from: https://ufhealth.org/colonoscopy
    15. UF Health: University of Florida Health [Internet]. Gainesville (FL): University of Florida Health; c2020. Sigmoidoscopy: Overview; [updated 2020 Dec 17; cited 2020 Dec 17]; [about 2 screens]. Available from: https://ufhealth.org/sigmoidoscopy
    16. UF Health: University of Florida Health [Internet]. Gainesville (FL): University of Florida Health; c2020. Stool guaiac test: Overview; [updated 2020 Dec 17; cited 2020 Dec 17]; [about 2 screens]. Available from: https://ufhealth.org/stool-guaiac-test
    17. UF Health: University of Florida Health [Internet]. Gainesville (FL): University of Florida Health; c2020. Virtual colonoscopy: Overview; [updated 2020 Dec 17; cited 2020 Dec 17]; [about 2 screens]. Available from: https://ufhealth.org/virtual-colonoscopy
    18. University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; c2020. Health Encyclopedia: Colorectal Cancer: Screening; [cited 2020 Dec 17]; [about 2 screens]. Available from: https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=34&contentid=16384-1
    19. UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2020. Colorectal Cancer Prevention and Screening; [updated 2017 Sep 9; cited 2020 Dec 17]; [about 2 screens]. Available from: https://www.uwhealth.org/coloncancerscreening/colorectal-screening-initiative-frequently-asked-questions/25338

    The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.