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bowel cancer screening

How accurate is bowel cancer screening?

Bowel cancer or colorectal cancer occurs due to the growth of polyps in the lining of the bowels. It is one of the most common types of cancer in Australia and might be treated with a high success rate if symptoms of bowel cancer are identified during the early stages. 

A bowel cancer screening may help doctors diagnose if the patient has bowel cancer or if the symptoms displayed are caused by a different gastrointestinal condition

That said, the accuracy of a cancer screening may depend on several factors such as the type of screening test you take and the preparation for it. 

When it comes to colorectal cancer screening, there are two types of tests available and in this post, we explore them in detail.

Stool-based tests

These tests examine the stool for possible signs of bowel cancer and can be taken at home, making most people prefer it over tests like a colonoscopy.

That said, stool-based tests may need to be done more frequently than clinical procedures to track abnormal growth. 

There are three types of stool-based bowel cancer screening tests. 

  • Faecal immunochemical test (FIT)

A faecal immunochemical test examines the stool to identify the presence of blood in the lower intestines, but may not detect bleeding from the upper parts of the digestive tract, such as the stomach. 

FIT tests can be taken at home, and the kits can be obtained from a local healthcare provider. 

This type of cancer screening may need to be done annually to track the growth of any abnormalities in the colon and the rectum. 

  • Guaiac-based faecal occult blood test (gFOBT)

A gFOBT is a test done to find hidden (occult) blood in the stool through a chemical reaction and, similar to a FIT test, may need to be done every year to track the bowel health of the patient.

A limitation of gFOBT is that the test may not be suitable to identify if the blood is from the colon or the upper parts of the gastrointestinal tract like the stomach. 

Certain foods and medications that are taken before the test may also alter the test results. 

Due to this, health experts recommend avoiding certain food items and medications before the test; including vitamin C, red meats, citrus fruits, and non-steroidal anti-inflammatory drugs.

  • Stool DNA test

When colorectal cancer or polyps grow, they often cause DNA mutations, which can be examined via a stool DNA test.

A stool DNA test looks for these abnormal sequences from cancer or polyp cells, as well as signs of hidden blood. 

Although stool DNA tests don’t need to be done as frequently as the other stool tests, patients may still need to undergo the test at least every three years for an accurate diagnosis.

It should also be noted that all three types of stool-based tests have certain limitations. There may be instances of false-positive results or instances where cancer and polyps may be missed. 

If any abnormal growth is identified, the patient may still be required to get a colonoscopy for further examination. 

Structural exams

Structural bowel cancer screening tests are used to examine the inside of the colon and rectum for any abnormalities. These exams do not need to be taken as often as stool-based tests and provide more accurate diagnoses. 

  • Colonoscopy

In a colonoscopy, a specialist examines the entire length of the colon and rectum by inserting a colonoscope through the anus. Polyps or other types of abnormal tissue can also be removed during a colonoscopy.

  • CT colonography 

A CT colonoscopy is an advanced type of CT scan that uses both X-rays and CT scans to get 3-dimensional images of the interior of the bowels to check if the colon and the rectum show any abnormal growths.

A colonoscopy may still be required to examine the area further and remove any growths that are detected.

  • Flexible sigmoidoscopy

While similar to colonoscopy, sigmoidoscopy is not used to examine the entire colon; instead, the test only examines the lower part of the colon. 

Images from the sigmoidoscope may help doctors identify any abnormalities and remove them if necessary. 

Among the structural exams, colonoscopies are the most common and are up to 94% accurate when it comes to a diagnosis. 

Even with the structural tests, there may still be a chance of missing small polyps, making it necessary to be regular with your screenings.

Regular bowel cancer screening is key to an early diagnosis

Regular bowel cancer screening in Australia is recommended for adults between the ages of 50 and 75, which are the ages that are most at risk. 

Seek immediate medical attention and get a cancer screening test done if you experience unexplained, sudden symptoms like pains in the anus or rectum, a lump in the anus or rectum, or blood in stools.