What is a colorectal cancer test, how to test it & what does it show?

The large bowel is a tube-like organ consisting if the colon and rectum. It connects the small intestine to the anus and is the end part of the digestive tract. Its key role is to remove water and certain nutrients from food that has been partly digested.

Colorectal cancer most commonly affects older adults and often starts with the formation of benign polyps in the colon. The condition can be diagnosed and treated effectively, particularly if it is diagnosed early.

This page highlights what the most common types of colorectal cancer tests are, how they are performed, and what the results may show.

What is a colorectal cancer test?

The most common types of colorectal cancer tests are as follows:

  • Colonoscopy: this test involves inserting a long, thin flexible tube called a colonoscope via the anus. A colonoscope has a video camera located at the tip of a long flexible tube, which allows the inside of the large bowel to be examined. This is one of the most sensitive tests to detect colorectal cancer and allows tissue samples (biopsies) to be taken if abnormalities are seen. However, it is an invasive process that requires thorough pre-test colon cleansing with diet changes and often sedation.
  • Virtual colonoscopy: this test is also sometimes called CT colonography as it involves using a CT scan to create an image of the large bowel. This isn’t as invasive as a standard colonoscopy but still requires a small flexible tube to be inserted a short way into the rectum. You may also have a small tube put into your arm to allow a bowel muscle relaxant to be given. Thorough pre-test bowel cleansing and diet changes are also required.
  • Faecal occult blood (FOB) or faecal immunochemical (FIT) tests: these tests are carried out by analysing a stool sample to establish the presence of blood in the stools. This test can is much less invasive than colonoscopies but has false-positive and false negative readings. Additional testing will be required if a positive result has been obtained.
  • Stool DNA test: This is a newer test which looks for DNA changes and blood in a stool sample. This test can is much less invasive than colonoscopies but has false-positive and false negative readings. Additional testing will be required if a positive result has been obtained.

It is recommended that individuals over 50 years old start routinely having colorectal cancer screening tests. However, you should get tested earlier if you are at an increased risk of developing colorectal cancer – for example if you have a family history of colorectal cancer or have previously had bowel cancer or pre-cancerous bowel polyps.

What does a colorectal cancer test show?

Abnormal results from a colorectal screening test could indicate that there is a problem with your large bowel. As a general guideline, colorectal cancer screening tests may show the following:

Test Normal results Abnormal results
Colonoscpopy and virtual colonoscopy  No irregularities Polyps, cancer, other bowel conditions such as diverticular disease
Stool DNA test No cell DNA changes detected Cell DNA changes or blood detected
FIT and FOB tests No blood detected Blood detected

If you have an abnormal result, your doctor may order further tests such as a biopsy to confirm whether it is cancer. It is important to note that abnormal results are not always a sign of colorectal cancer and may prove to be a false positive after further investigation.

Can colorectal cancer be detected with a blood test?

There are currently no reliable blood tests available to establish whether you may have colorectal cancer. However, a blood test can help assess your overall health and indicate whether your organs are functioning well.

Are there any symptoms of colorectal cancer?

Colorectal cancer is may have no symptoms in the early stages. However, symptoms can develop over time. These may include:

  • Bleeding from the back passage or blood in one’s poo
  • A change in one’s normal bowel habit such pooing more often, looser poo or constipation
  • Abdominal pain
  • Feeling that the bowels do not completely empty during a bowel movement.
  • Tiredness
  • Weight loss

What do stools look like in colorectal cancer?

Although stools can look perfectly normal in individuals with colorectal cancer, any red, dark red or black stool should be investigated as they could be a sign of colorectal cancer.

How can I get tested for colorectal cancer?

You can get screened for colorectal cancer at home with a single faecal immunochemical test (FIT) home test kit. All you need to do is order your kit, take your own sample, send it back in our pre-addressed return envelope, and wait to receive your results online within 8 days.

Alternatively, you can book a health check with one of our Certified Healthcare professionals at one of over 2,000 mobile clinics nationwide. Our Male Cancer Risk Package and Female Cancer Risk Package include a FIT test, in addition to a wide array of health markers for a detailed view of your health. These include key readings that play an essential role in maintaining men’s general health, as well as assessing  your risk for other types of cancers.