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Screening for Colorectal Cancer


Colorectal cancer (CRC) screening tests help to identify if you have or are developing colorectal cancer.

The majority of colorectal cancers begin as a small growth on the bowel wall – a colorectal polyp or adenoma. These, often mushroom-shaped, growths are usually benign but some develop into cancer over time. If left untreated they can grow into the muscle layer underneath and then through the bowel wall.

Finding and removing polyps may prevent colorectal cancer and colorectal cancer is generally more treatable and curable when it is diagnosed early before it has had a chance to spread. This makes screening for colorectal cancer so important and why everyone over the age of 50 should be screened.

Screening tests help find some types of cancer before you have any symptoms

It is important to take these tests even if you feel well and you have a healthy lifestyle. They should be part of your regular medical care.

In many European countries, if you are in a certain age or population group, you are invited for regular screening tests that can help identify colorectal cancer at an early stage, before you have even noticed that something might be wrong. Early detection is very important and that is what screening is designed for!

Take control of your health - see your doctor regularly and know when you should be screened for colorectal cancer.

Screening: Benefits and Limitations

Screening for colorectal cancer has benefits!

  • It can help detect colorectal cancer at its earliest stage, when there is a 90% (9 in 10) chance of curing it
  • It can prevent some colorectal cancers from developing
  • By participating in colorectal cancer screening mortality is reduced by 24%

Screening for colorectal cancer has limitations!

  • No screening test is 100% accurate
  • Be aware - you should always go to see your doctor if you have any suspicious symptoms, even if you had a negative screening result
  • Screening is only recommended for people who are not experiencing symptoms that may indicate colorectal cancer. If you are experiencing symptoms such as blood in your stool,  unexplained abdominal pain, change in bowel habits or weight loss, talk to your doctor about a referral for diagnostic testing to determine the cause of these symptoms
  • Sometimes test results suggest you have cancer, an adenoma or a polyp even though it proves not to be the case. In these circumstances you will be advised to have a follow up colonoscopy. It is very important that you attend the appointment as it could save your life!

Screening Options

There are various screening options available – the main ones are described below. To decide which screening option is right for you, please talk to your doctor.

  1. Stool Tests

    A stool test is any easy test that checks your stool for blood. Some people find this embarrassing but it could save your life – it is that simple. Polyps or cancer in the colon or rectum have blood vessels that may release a small amount of blood that is picked up by the stool as it passes through the colon. Stool tests check for traces of this hidden (occult) blood which cannot be seen by eye.


    The faecal occult blood test, also called FOBT, is the main screening method recommended in the EU.
    There are three types:

    • Guaiac FOBT (gFOBT)
      This test uses a chemical to detect haem, a component of the blood protein haemoglobin. The chemical will cause a reaction on a paper card to find traces of blood in the stool.

      Various foods, dietary supplements and medications can, rarely,  affect the results of this faecal occult blood test — either indicating that blood is present when it isn't (false-positive) or missing the presence of blood that's actually there (false-negative).

      You might be asked to redo the test and to avoid certain foods or medicines before doing it. To ensure accurate test results, follow your doctor's or the leaflets’ instructions carefully.

    • FIT - Faecal Immunochemical Test (or iFOBT)
      This test uses specific antibodies to detect human globin protein which is part of haemoglobin. Dietary restrictions are typically not required for FIT and the test can detect the presence of blood at concentrations 100 times lower than can the guaiac test.

    • Stool DNA test (also known as a multitargeted stool DNA test or MT-sDNA)
      This test currently requires a full faecal stool sample and combines FIT with a test that detects both altered DNA in the stool and small amounts of blood shed into the stool from colon or rectal cancer or polyps. The DNA changes are found in very tiny amounts, so very sensitive laboratory methods are required to detect them. The test is set to be very sensitive and therefore has a higher false positive rate than FIT.

    The gFOBT and FIT are widely used and both are proven to indicate the risk of colorectal cancer thus reducing deaths from this disease. However, gFOBT has largely been replaced by the more accurate and sensitive FIT as recommended in the EU guidelines. The FIT is the more accurate of the two and is more likely to detect bleeding polyps than gFOBT.

    Both types of test are simple and quick to carry out in the privacy of your home. FIT test

    How about the results?

    • Negative result - A screening test is considered negative if no blood is detected in your stool samples.
    • Positive result - A screening test is considered positive if blood is detected in your stool samples and you will need an additional investigation – usually colonoscopy - to look for the source of the (microscopic) bleeding.

    When should you start screening?

    It is generally recommended that programmes commence screening at age 50 and continue to age 75 sometimes with an option to extend it beyond 75.

    How often should this be done?

    It is recommended to repeat this test once every one or two years.

  2. Colonoscopy

    A colonoscopy is another option for colorectal cancer screening. This test is one of the most sensitive currently available as it allows the doctor to directly view the rectum and the entire colon and detect changes or abnormalities in the large intestine (colon) and rectum.

    During a colonoscopy a long, flexible tube (colonoscope) is inserted into the rectum.

    The scope - which is long enough to reach the entire length of your colon - contains a light and a tube (channel) that allows the doctor to pump air or carbon dioxide into your colon. The air or carbon dioxide inflates the colon which provides a better view of the lining of the colon.

    The camera sends images to an external monitor so that the doctor can study the inside of your colon.

    Instruments can be inserted through the channel to take tissue samples (biopsies) or remove polyps or other areas of abnormal tissue.

    A colonoscopy typically takes about 30 to 60 minutes.


    How about the results?

    Your doctor will review the results of the colonoscopy and then share the results with you.

    • Negative result
      A colonoscopy is considered negative if the doctor doesn't find any abnormalities in the colon
    • Positive result
      A colonoscopy is considered positive if the doctor finds any polyps or abnormal tissue in the colon

    Most polyps are not cancerous, but some can be precancerous. Polyps removed during colonoscopy are sent to a laboratory for analysis to determine whether they are cancerous, precancerous or noncancerous.

    How often should this be done?

    Most people who have had certain types of polyps removed during a colonoscopy will need to get a colonoscopy again after 3 years, but some people might need to get one earlier (or later) than 3 years, depending on the type, size, and number of polyps.
    People who have had colon or rectal cancer may need to have  further colonoscopies. Other procedures like ultrasound might also be recommended for some people with rectal cancer, depending on the type of surgery they had.

  3. Flexible Sigmoidoscopy

    In this test, the rectum and part of the colon are examined using a flexible lighted instrument which is inserted into the rectum.

    This examination is used to evaluate the lower part of the large intestine (colon).

    The sigmoidoscope contains a light and a tube (channel) that allows the doctor to pump air or carbon dioxide into your colon. The air expands the colon, which provides a better view of the colon lining.

    The instrument also contains a tiny video camera at its tip. The camera sends images to an external monitor so that the doctor can study the inside of your colon. The doctor can also insert instruments through the scope to take tissue samples (biopsies).

    A flexible sigmoidoscopy examination typically takes about 15 minutes.

    How about the results?
    Your doctor will review the results of your flexible sigmoidoscopy examination and then share them with you.

    Negative result.
    The results of a flexible sigmoidoscopy exam are considered negative if the doctor doesn't find any abnormalities in the colon.
    Positive result.
    The results of a flexible sigmoidoscopy exam are considered positive if the doctor finds polyps or abnormal tissue in the colon. Depending on the findings you may need additional testing - such as a colonoscopy - so that any abnormalities can be examined more thoroughly, biopsied or removed.

    How often should this be done?

    If you are at average risk of colorectal cancer - you have no colorectal cancer risk factors other than age - your doctor may recommend waiting five years before repeating the examination.

  4. Other Screening Methods

    • CT (computed tomography) scan/ virtual colonoscopy
      The CT colonography or virtual colonoscopy uses X-Rays and computers to take 2 or 3 dimensional images of the colon and rectum. It is less invasive than a colonoscopy and usually does not require sedation other than a liquid diet and bowel preparation beforehand. Polyps cannot be removed during this screening process which means that a follow up a colonoscopy will be needed if the test is positive.

      Depending on the results of the examination re-screening may be needed every 10 years.


    • Capsule endoscopy
      With capsule endoscopy, a digital video camera with the size and shape of a pill is swallowed to visualise the gastrointestinal tract. It is usually used to examine the small intestine or oesophagus. The procedure requires a liquid diet and bowel preparation. This test is not widely available and is as yet not as effective as colonoscopy in detecting polyps and cancer.

      As this is a newer type of test the best length of time to go between tests is not yet clear.


Signs and Symptoms of Colorectal Cancer

As mentioned in the introduction, screening tests help to identify the risk of developing some types of cancer before you have any symptoms.

Even if you are tested regularly, knowing the signs and symptoms of colorectal cancer is very important.  Colorectal cancer is highly treatable if it is diagnosed in its early stages.

Colorectal cancer might not cause symptoms right away but if it does the common symptoms may include:

  • An ongoing change in bowel habits that lasts for more than a few days (diarrhea, constipation or feeling that the bowel does not empty completely)
  • Stools that are narrower than usual
  • Blood (either bright red or very dark) in the stool
  • Rectal bleeding with bright red blood
  • Frequent gas pains, bloating, fullness or abdominal cramps
  • Weight loss for no known reason
  • Feeling very tired (weakness and fatigue)

Some colorectal cancer symptoms are mostly noticeable through changes in your digestive tract but others can impact your entire body.

ab pain

These can vary based on the person and the signs will also differ in severity based on the cancer’s location in the colon or rectum and size and growth.

If you have any signs or symptoms of colorectal cancer…….. do not ignore them! 

Check with your doctor if you experience any of the above, regardless of your age.

Other conditions

It is pretty common for other conditions to mimic some colorectal cancer symptoms. An infection, Crohn’s disease, Ulcerative Colitis and other gastrointestinal problems can create similar symptoms.

It is very important to know your body and speak with your doctor to discover the cause of your symptoms and seek treatment.
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The information contained in this website is for general health education purposes only. Its objective is to give general guidance, and should not replace or be interpreted as a consultation with a physician or a healthcare professional. For any personal questions about your health, please talk to your doctor. Even if we try to keep the information on our website up-to-date and correct, we cannot guarantee that it covers all the latest medical and scientific insights.
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