(Examination of the large bowel)
What is Colonoscopy?
A colonoscopy is an internal examination of the colon (large
intestine) using an instrument called a colonoscope. The colonoscope
is a small camera attached to a flexible tube which is used to
examine the entire length of the colon.
How is the test performed?
You will lie on your side or back as the doctor slowly passes the
colonoscope along your large intestine to look at the lining. Your
doctor will, again, examine the lining as the colonoscope is taken
out. Air will be inserted through the scope to provide a better
view. Suction may be used to remove secretions. Tissue samples may
be taken with tiny biopsy forceps inserted through the scope. Polyps
may be removed with electrocautery snares. Photographs may be taken.
Specialized procedures, such as injection therapy, clipping, and
tattooing to better localize lesions may be performed.
How to prepare for the test?
Thorough cleansing of the bowel prior to colonoscopy is very
important so that the procedure can be accurate and complete. You
will be given detailed instructions for doing this. A bowel
preparation is made up of either drinking a large quantity of a
special cleansing drink, or may involve a combination of laxative
pills and a clear liquid drink. To avoid dehydration during this
preparation phase, you will be asked to drink plenty of clear
liquids such as juices and broths. Preparation for colonoscopy can
very rarely cause kidney problems.
What about the medications I am taking?
You should be able to continue taking your usual medications with
some exceptions. Please tell your health care provider what you are
taking and particularly if you are taking:
Blood thinners such as Coumadin/Warfarin
Since your health care provider may ask you to stop or change the
doses of these medicines before the procedure.
Please also tell your health care provider if you have:
- a joint replacement
- a heart valve replacement
Since antibiotics may be needed before the procedure.
How will the test feel?
Just before the procedure, you will be given a sedation medication
and a pain killer by vein. This will produce relaxation and a drowsy
feeling. You may feel pressure as the scope moves inside. Brief
cramping and gas pains may be felt as air is inserted or as the
scope is advanced. The passing of gas is expected and necessary.
After the exam there may be abdominal cramping and considerable
passing of gas may occur. Because of the sedation, you may have no
memory of the test. Sedation should typically wear off in a few
WHAT IF THE DOCTOR FINDS SOMETHING WRONG?
Your doctor may pass an instrument called a biopsy forceps through
the colonoscope and take a small piece of bowel lining to look at
under the microscope. If colonoscopy is being done to find bleeding
sites, your doctor may stop the bleeding through the colonoscopy by:
- injecting drugs
- sealing off bleeding vessels with heat treatment or other methods
such as small clips or liquid injection.
Your doctor may also find polyps which will most likely be removed
or biopsied during the procedure.
What are polyps and why are they
Polyps are growths in the bowel lining and they can be as small as a
tiny dot or up to several centimeters big. They are not usually
cancer but can grow into cancer over time. The doctor usually
removes a polyp through the colonoscope using a wire loop or snare
to separate the polyp from the bowel wall. An electric current is
What are the risks of colonoscopy?
(a) Bowel perforation – the bowel wall may be punctured. This can
cause leakage of bowel contents into the abdominal cavity. The risk
is approximately 1 to 2 per 1000 tests but may be higher when polyps
are removed, particularly with large polyps. This is treated by
keeping the bowel empty using suction and a tube passed into the
stomach or bowel via the nose. Fluids and antibiotics are given via
an intravenous drip. This will require a hospital stay. A surgical
repair operation requiring a longer hospital stay may be needed.
(b) Heavy or persistent bleeding from biopsy or polyp – removal
sites. This may be immediate or may be delayed by as much as two
weeks. The bleeding may stop on its own or may require additional
therapies through the colonoscope. Very rarely, surgery may be
needed to stop bleeding which cannot be stopped via these means.
Very rarely, a blood transfusion may be needed if there is a lot of
(c) Having a normal colonoscopy does not guarantee that you do not
have or will not get colon cancer. Polyps or cancer can be missed.
This risk is higher if your bowel is not cleaned properly. It is
very important that you follow the instructions to clear your bowel
before the procedure.
(d) Adverse reaction to sedative medication causing breathing
problems or low blood pressure is very rare. Also very rarely, heart
and lung problems can occur such as low oxygen levels and lowered
blood pressure. People with underlying ill health are more at risk.
(e) Nausea, vomiting, bloating or rectal irritation can occur during
the preparation phase from medications that cleanse the bowel. If
nausea, vomiting or bloating occurs, stop the preparation for 1 to 2
hours and then begin again very slowly, if possible, until the bowel
is cleansed thoroughly.
(f) Death due to complications of colonoscopy is extremely rare.
What if I do not have the
A serious colon problem can be missed such as a polyp, tumor, or
inflammation of the bowel.
Are there other tests I could have
There are a number of other tests that could be done such as
flexible sigmoidoscopy, double contrast barium enema, virtual
colonoscopy utilizing a CT Scan, and stool tests to detect hidden
blood and to look for abnormal DNA.