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HealthInfo West Coast-Te Tai Poutini

Bowel cancer screening

Bowel polypsMost bowel cancers develop from a tiny growth, or polyp, that slowly gets bigger over many years.

Your bowel can have different types of polyps. Most polyps aren't cancer (they are benign) and don't grow into a cancer. But some could grow into a cancer if they're left alone and are called precancerous. Adenomatous polyps are in this group that could grow into cancer.

If we remove a precancerous polyp, we can prevent a bowel cancer. It is also possible to pick up bowel cancer before you have any symptoms. Finding a bowel cancer early means it is more likely to be curable and you are less likely die from it.

What bowel cancer screening is

Bowel cancer screening is when you have tests to look for an early cancer, or precancerous polyp, before you have any symptoms from it.

Faecal occult blood test

A special test on your stool (bowel motion, or poo) called a faecal occult blood test (or FOB) is recommended by specialists to be used only as part of a supervised screening programme. This is because it's not always accurate.

This test looks for microscopic amounts of blood in your poo. Bowel cancers can bleed when they grow, so the test may find tiny amounts of blood before you have any symptoms.

A positive FOB test result is quite common and doesn't necessarily mean that you have bowel cancer. And a negative result doesn't necessarily mean you don't have cancer.

If you have done a self-bought test and it is positive, tell your GP. They are likely to talk with you to see if you have any symptoms, examine you and do a blood test to see if you have iron deficiency anaemia.

You may not qualify for further publicly funded tests. If you don't qualify, talk to your GP about your options and follow-up plan.

Colonoscopy or CT colonogram

There are two main techniques used to look for bowel cancer. The first is a colonoscopy. This procedure happens after an injection of medication to relax you. A flexible tube (also called an endoscope) is put through your anus to look at your bowel.

The second is a special CT scan called a CT colonogram. In this procedure, your bowel is filled with gas, using a tube put through your anus. You then move into different positions while scans are made. A CT colonogram takes about 15 minutes.

For both techniques you need to do some preparation to clear out your bowel. They have different pros and cons, but both can have serious, but rare, side effects.



CT colonography

Preparing at home

You will need to empty your bowel with one day of fasting and laxatives

You will be on a clear, liquid diet for one to three days. You may need a laxative.

Medication on the day

You will be sedated before the colonoscopy. A colonoscopy can be done without sedation but may be quite uncomfortable.

You will have to drink an oral preparation for the scan.

Time needed for the test

You will need to allow most of the day.

Including preparation and recovery it will take about one hour.

If the test finds polyps

The polyps can be removed during the colonoscopy.

You will have to have a colonoscopy afterwards to remove the polyps.


There is a very small (one in 1000), but serious, risk of making a hole in your bowel (called perforation).

You will receive a small dose of radiation (about four times the amount of naturally occurring radiation you get every day). There is a much smaller risk of perforation, which is very rare

Next steps

Because of the sedation, you won't be able to drive or sign legal documents for 24 hours afterwards.

Because you haven't had any sedation you can drive afterwards.

If you are paying for either of these, you may want to know that a CT colonogram is much cheaper than a colonoscopy.

The American site UpToDate has information about the different screening methods used for colon cancer, how effective they are, and what the risk factors for colon cancer are.

This New Zealand leaflet is for people who have a higher risk of bowel cancer. It has specific information for people who've had adenomatous polyps, previous bowel cancer, inflammatory bowel disease, or who have a family history of bowel cancer. It tells you what bowel cancer is, what the symptoms are, how common it is, what you can do to reduce your risk of bowel cancer, and tests to check for bowel cancer.

Who should have bowel cancer screening

There are pros and cons of screening. One disadvantage is the potential for rare but serious side effects from a test such as a colonoscopy.

International guidelines do advise most people should have bowel cancer screening from the age of 50 to 75. A national bowel screening programme is being introduced to New Zealand between 2017 and 2020. It isn't available on the West Coast yet. For more information, see Time to Screen's page about the programme.

On the West Coast, certain people at high risk of bowel cancer can get publicly funded screening. If anyone in your family has had bowel cancer, if you have had bowel cancer or bowel polyps, or if you have inflammatory bowel disease, talk to your GP about whether you qualify.

If you don't qualify for publicly funded bowel cancer screening, talk to your GP about your options. You may choose to pay to have private bowel cancer screening.

Information provided by the Canterbury DHB. Adapted by the West Coast DHB. Last reviewed April 2019.


Page reference: 204760

Review key: HIBWC-17275