The American Cancer Society and the
Centres for Disease Control and Prevention recommend that men and women at
average risk of developing colorectal cancer (i.e. no family history and few,
if any, other risk factors) should begin screening for colorectal cancer from age
Tests to screen for polyps and
colorectal cancer can be divided into two broad groups: tests to find
colorectal polyps and cancer and tests that mainly find cancer. Some of these
tests are invasive, while others are simple blood tests.
A double contrast barium enema
involves an x-ray examination of the large intestine (colon and rectum). A contrast
material, a chalky substance, is poured through a thin tube inserted into the
anus to partly fill and open up the colon. Air is pumped in, causing the colon
to expand and allowing good x-ray pictures to be taken. If an area does not
look normal, patients will need to have a colonoscopy.
The American Cancer Society recommends
that this test be done every five years.
Flexible sigmoidoscopy (flex-sig):
A thin, flexible, lighted tube with a small camera attached is placed into the
lower part of the colon, allowing the doctor to look inside the rectum and at part
of the colon.
Due to its size, the doctor is only
able to see about half of the colon. If a small polyp is found, the doctor may
remove it with tools used through the scope. If a bigger polyp or colorectal
cancer is found, a colonoscopy will be necessary.
This test usually takes 10 – 20
minutes and is recommended to be done administered every five years.
In a colonoscopy, a colonoscope, a
longer version of the flex-sig, is used the same way but allows the doctor to
see the entire colon. If a polyp is found, the doctor may remove it. If
anything else looks abnormal, a biopsy might be done. This test usually takes
about half an hour and a sedative is given beforehand. It is recommended that
this test be administered every 10 years.
Virtual colonoscopy: A thin tube is
inserted and either an MRI or a CT scanner takes pictures of the colon. Special
computer programmes create both two-dimensional x-ray pictures and a 3-D view
of the inside of the colon and rectum, allowing the doctor to look for polyps
This is an alternative to tests where
a tube or scope is put in the colon or rectum. However, if polyps or other
problems are seen, a colonoscopy will likely be needed to remove or better
Next week: Tests that find colorectal cancer and reducing your risk