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Bowel cancer screening
Most 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
actually 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 is bowel cancer screening?
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
These 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.
HealthInfo reference: 180522
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Issued: 22 June 2016
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Bowel cancer screening
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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.
Colonoscopy versus CT colonography – weighing up which is right for you
Colonoscopy
CT colonography
How do I prepare
You will need to empty your bowel with You will be on a clear, liquid diet for one to
at home?
one day of fasting and laxatives.
three days. You may need laxatives.
What medication
You will have to drink an oral preparation for
will I need on the
You will be sedated before the
colonoscopy. A colonoscopy can be
day?
done without sedation but may be
How much time
You will need to allow most of the day. Including preparation and recovery it will
the scan.
quite uncomfortable.
take about one hour.
will it take on the
day?
What happens if it The polyps can be removed during the
colonoscopy.
finds polyps?
What is the major
risk?
You will have to have a colonoscopy
afterwards to remove the polyps.
There is a very small (one in 1000), but You will receive a small dose of radiation
serious, risk of making a hole in your
(about four times the amount of naturally
occurring radiation you get every day). There
is a much smaller risk of perforation, which
bowel (called perforation).
is very rare.
What happens
Because of the sedation, you won't be
Because you haven't had any sedation you
afterwards?
able to drive or sign legal documents
can drive afterwards.
for 24 hours 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 (www.updtodate.com) has information about the different screening
methods used for colon cancer, how effective they are, and what the risk factors for colon cancer are.
(Search for “colon cancer screening”, choose patient information.)
There is a New Zealand leaflet 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. Go to www.health.govt.nz and search for “Information for people at increased
risk of bowel cancer”.
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Issued: 22 June 2016
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Bowel cancer screening
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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. Some countries have national screening for bowel cancer, but we don't yet have a national
screening programme in New Zealand (as we have for breast and cervical cancer).
In Canterbury, 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.
Written by HealthInfo clinical advisers. Adapted by clinical director, Gastroenterology, Canterbury DHB.
Updated June 2015.
180522
HealthInfo reference: 180522
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Issued: 22 June 2016
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