Tests to find cancer in the bowel

The main test used to look for bowel cancer is a colonoscopy. Less commonly used tests are CT colonography and flexible sigmoidoscopy.

Learn more about:

• Colonoscopy, polypectomy and biopsy
• Less commonly used tests

Colonoscopy, polypectomy and biopsy

A colonoscopy lets your doctor look at the lining of the entire large bowel. Before a colonoscopy, you clear out the bowel with a preparation. It’s very important to follow the instructions – the cleaner the bowel, the more likely it is that the doctor can see polyps or areas of concern.

Most colonoscopies are done as day surgery at a hospital. On the day of the procedure, you will usually be given a sedative or light anaesthetic so you don’t feel anything. This will make you drowsy or may put you to sleep. A colonoscopy usually takes 20–30 minutes.

During the procedure, the doctor puts a colonoscope (a flexible tube with a camera on the end) through your anus and up into the rectum and colon. Carbon dioxide or air is passed through the colonoscope to inflate the colon and make it easier for the doctor to see the bowel.

Polypectomy

During the colonoscopy, any precancerous polyps will be removed – this is called a polypectomy. Most polyps are small (less than 1 cm) and the procedure is very safe and usually has no side effects.

Biopsy

If the doctor sees abnormal-looking areas, including polyps, they will remove a sample of the tissue. This is called a biopsy. A pathologist looks at the sample under a microscope to check for cancer or specific gene changes. For more on this, see Genomic testing.

Side effects

You may be weak or drowsy so someone will need to take you home afterwards. You won’t be able to drive until the day after your procedure. The gas used to inflate the bowel can sometimes cause bloating or wind pain. Rare complications include bleeding, or damage to the bowel (perforation) or spleen. Your doctor will explain the risks.

Less commonly used tests

CT colonography

Also called a virtual colonoscopy, it uses a CT scanner to create images of the colon and rectum. Bowel preparation is usually needed before the test. A CT colonography is done by a radiologist, (who analyses x-rays and scans).

You may have a CT colonography if a colonoscopy didn’t show all of the colon or when a colonoscopy is not safe. However, a CT colonography is not often used because it exposes you to radiation and is not as accurate as a colonoscopy. It can see only bigger polyps, not small ones.

If any abnormality is detected, you will need to have a colonoscopy so that the doctor can take tissue samples. A CT colonography is covered by Medicare only in limited circumstances.

Flexible sigmoidoscopy

This test is similar to a colonoscopy but only lets the doctor see the rectum and about the lower half of the colon (sigmoid and descending colon). Before a flexible sigmoidoscopy, you will need to have a light bowel clean-out, usually with an enema). You may be given light sedation for the procedure.

You will then lie on your left side while a colonoscope (or, sometimes, a shorter but similar tube called a sigmoidoscope) is put into your anus and guided up through the bowel. The colonoscope or sigmoidoscope blows carbon dioxide or air into the bowel to inflate it slightly so the doctor can see the bowel wall more clearly.

A light and camera at the end of the colonoscope or sigmoidoscope show up any unusual areas or polyps, and your doctor can take tissue samples (biopsies).

→ READ MORE: Further tests for bowel cancer

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