Describes colonoscopy, a screening test that examines the lining of the large intestine. Explains that the test is done to look for polyps in the colon or rectum and to check for colorectal cancer. Discusses preparing for the test and how it is done.
Colonoscopy is a test that allows your doctor to look at the inner
lining of your
large intestine (rectum and colon). He or she uses a thin, flexible tube
called a colonoscope to look at the colon. A colonoscopy helps find
colon polyps, tumors, and areas of inflammation or
bleeding. During a colonoscopy, tissue samples can be collected (biopsy) and abnormal growths can be taken out.
Colonoscopy can also be used as a screening test to check for cancer or
precancerous growths in the colon or rectum (polyps).
colonoscope is a thin, flexible tube that ranges from
48 in. (125 cm) to
72 in. (183 cm) long. A small
video camera is attached to the colonoscope so that your doctor can take
pictures or video of the large intestine (colon). The colonoscope can be used
to look at the whole colon and the lower part of the small intestine. A test
sigmoidoscopy shows only the
rectum and the lower part of the colon.
Before this test, you will need to clean out your colon (colon prep).
Colon prep takes 1 to 2 days, depending on which type of prep your doctor
recommends. Some preps may be taken the evening before the test. For many people, the prep is worse than the test. The bowel prep may be uncomfortable, and you may feel hungry on the clear liquid diet. Plan to
stay home during your prep time since you will need to use the bathroom often.
The colon prep causes loose, frequent stools and diarrhea so that your colon
will be empty for the test. If you need to drink a special solution
as part of your prep, be sure to have clear fruit juices or soft drinks to
drink after the prep because the solution may have a salty or unpleasant taste.
Colonoscopy is one of many tests that may be used to screen for colon cancer. Other tests include sigmoidoscopy, stool tests, and computed tomographic colonography. Which screening test you choose depends on your risk, your preference, and your doctor. Talk to your doctor about what puts you at risk and what test is best for you.
This test is recommended by the American
Cancer Society (ACS), the American College of Gastroenterologists (ACG), the
American Gastroenterological Association (AGA), and the U.S. Preventive
Services Task Force (USPSTF).
These groups recommend routine
testing for people age 50 and older who have a normal risk for colorectal
Your doctor may recommend earlier or more frequent testing if you have a higher risk of colorectal cancer. Talk to your doctor about when you should be tested.
Check for the cause of blood in the stool or
Have bleeding problems or
take aspirin or other blood thinners.
Had an X-ray test using barium, such as a barium enema, in the
last 4 days.
Are or might be pregnant.
You may be asked to stop taking aspirin products or iron
supplements 7 to 14 days before the test. If you take blood-thinning medicines
regularly, discuss with your doctor how to manage your medicine.
You will be asked to sign a consent form that says you understand the
risks of the test and agree to have it done.
Talk to your doctor about
any concerns you have regarding the need for the test, its risks, how it will
be done, or what the results will mean. To help you understand the importance
of this test, fill out the
medical test information form(What is a PDF document?).
Arrange to have someone take you home after the test,
because you may be given a medicine (sedative) to
help you relax before the test.
Before this test, you will need to
clean out your colon. The following information gives you a general idea of the
preparation for a colonoscopy. Your doctor will give you specific instructions
before your test.
One to two days before a colonoscopy, you will stop eating solid
foods and drink only clear fluids, such as water, tea, coffee, clear juices,
clear broths, flavored ice pops, and gelatin (such as Jell-O). Do not drink anything
red or purple, such as grape juice or fruit punch. And do not eat red or purple
foods, such as grape ice pops or cherry gelatin.
Your doctor will recommend a medicine for you to use to prepare for your colonoscopy. It will most likely be a prescription
laxative tablet and/or a laxative solution (such as Nulytely or Golytely) that you drink before your colonoscopy. This solution will be given to you as a powder
that you will mix with
1 gal (3.8 L) of water. You may need to drink this laxative solution over 1 to 2 hours in the evening before the test. Or you may be asked to drink half the solution the evening before your test and the other half the morning of your test. This solution
may taste very salty and may make you feel sick to your stomach. To make your
colon prep easier, you may want to try some of the following tips:
You may find it easier to drink the solution if you use a straw with the end at the back of your throat (to bypass the taste buds).
Each time you drink some of the solution,
you may also drink some water or clear fluids (like apple juice) to help get
rid of any unpleasant taste in your mouth.
your doctor if it is okay for you to add flavored drink crystals (such as
Crystal Light) to the solution.
Add lemon juice to the solution or
suck on sliced lemon wedges after you take a drink.
You may find it easier to
drink the solution if you chill it in the refrigerator first.
Your doctor may recommend a different preparation product, such as the
Nutraprep meal kit or sodium phosphate tablets (for example, Visicol). These are other methods
of preparing for a colonoscopy. If you are concerned about the standard bowel prep, you can ask your doctor whether another method will
work for you.
Oral sodium phosphate (either tablets or liquid) can cause kidney problems. Make sure you check with your doctor before using a nonprescription sodium phosphate product.
You will want to stay home while doing the colon prep, because the colon prep will make you use the bathroom
Drink plenty of clear fluids during the prep so you will not
dehydrated. This will also help clean out your colon
completely after you finish the colon prep.
Do not eat any solid
foods after doing the colon prep.
Stop drinking clear
liquids 6 to 8 hours before the colonoscopy.
How It Is Done
Colonoscopy may be done in a doctor's
office, clinic, or a hospital. The test is most often done by a doctor who
works with problems of the digestive system (gastroenterologist). The doctor may also have an
assistant. Some family doctors, internists, and surgeons are also trained to do
During the test, you may get a pain medicine and a
sedative put in a vein in your arm (IV). These
medicines help you relax and feel sleepy during the test. You may not remember
much about the test.
Before the test
You will need to take off most of your
clothes. You will be given a gown to wear during the test.
may lie on your left side with your knees pulled up to your belly. Because you will be given medicine during the colonoscopy, you probably won't remember much, if anything, until you wake up after the procedure.
Next, the doctor
will insert a thin, flexible colonoscope in your anus and move it slowly
through the rectum and into your colon. Air will be used to inflate your colon so the doctor can look at the lining of the colon through the
scope or on a computer screen hooked to the scope.
During the test
You may feel
the need to have a bowel movement while the scope is in your colon. You may
also feel some cramping. Breathe deeply and slowly through your mouth to relax
your belly muscles. This should help the cramping. You will likely feel and
hear some air escape around the scope. There is no need to be embarrassed about
it. The passing of air is expected. You may be asked to change your position
during the test.
Your doctor will look at the whole length of your
colon as the scope is gently moved in and then out of your colon.
The doctor may also
use tiny tools, such as forceps, loops, or swabs, through the scope to collect
tissue samples (biopsy) or take out growths. Usually, people do not feel
anything if a biopsy is done or if polyps are taken out.
scope is slowly pulled out of your anus and the air escapes. Your anal area
will be cleaned with tissues. If you are having cramps, passing gas may help
The test usually takes 30 to 45 minutes, but it may
take longer, depending upon what is found and what is done during the
After the test
After the test, you may need to stay at the clinic for 1 to 2 hours. Or you may be allowed to leave sooner with the person who will be driving you home. Your doctor will tell you when you can
eat your normal diet and do your normal activities. Drink a lot of fluid after
the test to replace the fluids you may have lost during the colon prep, but do
not drink alcohol.
If you received a
sedative during the test, do not drive, operate
machinery, or sign legal documents for 24 hours after the test. Arrange to have
someone drive you home after the test.
How It Feels
The colon prep will cause diarrhea. Some people also have cramping.
During the test,
you may feel very sleepy and relaxed from the sedative and pain medicines. You
may have cramping or feel brief, sharp pain when the scope is moved or air is
blown into your colon. As the scope is moved up the colon, you may feel the
need to have a bowel movement and pass gas. If you are having pain, tell your
The suction machine used to remove stool (feces) and
secretions may be noisy but does not cause pain.
You will feel
sleepy after the test for a few hours. Many people say they do not remember
very much about the test because of the sedative.
After the test,
you may have bloating or crampy gas pains and may need to pass some gas. If a
biopsy was done or a polyp taken out, you may have traces of blood in your
stool (feces) for a few days. If polyps were taken out, your doctor may
instruct you to not take aspirin and
nonsteroidal anti-inflammatory drugs (NSAIDs) for 7 to
There is a small chance for problems from a
colonoscopy. The scope or a small tool may tear the lining of the colon or
After the test
After the test, call your doctor
immediately if you:
Have heavy rectal bleeding.
severe belly pain.
Develop a fever.
Have a swollen and firm
Colonoscopy is a test that allows your
doctor to look at the inner lining of your
large intestine (rectum and colon). If a sample of tissue (biopsy) was collected during the colonoscopy, it will
be sent to a lab for tests.
Samples of colon tissue are usually sent to a
pathology lab, where they are looked at under a microscope for
Other samples of colon tissue may be sent to a
microbiology lab to see whether an infection is present.
Your doctor may be able to tell you the results immediately
after the procedure. Other test results are ready in 2 to 4 days. Test results
for certain infections may be ready in several weeks.
The lining of the colon looks
smooth and pink, with a lot of normal folds. No growths, pouches, bleeding, or
inflammation are present.
Reasons you may not be able to
have the test or why the results may not be helpful include:
barium enema within a week before the test. Barium can
block your doctor's view of the colon.
Not doing a good colon prep before the test. If you still have stool (feces) in the
colon, your doctor may cancel the test and you will have to reschedule and do the colon prep again.
Having a colon that has many turns, past surgery on the colon, or a lot of pain
during the test.
Taking iron supplements. This may make your stool
turn black and make it hard to clean out the colon. Do not take iron
supplements for several days before a colonoscopy.
Drinking red or purple fluids, such as grape juice or fruit
Eating red or purple foods, such as grape ice pops or
What To Think About
In general, pregnant women and people who have
an abdominal infection or
an attack of diverticulitis should not have a colonoscopy unless
there is an important reason for it.
Colonoscopy is a more
expensive procedure than a stool test or other endoscopic colon test (such
as sigmoidoscopy), but it can be done less often over time if
results are normal.
Experts recommend routine colon cancer testing
for everyone age 50 and older who has a normal risk for colon
Your doctor may recommend earlier or more frequent testing if you have a higher risk for colon cancer. Talk to your
doctor about when you should be tested.
Other screening tests for colon cancer include sigmoidoscopy, stool tests, and computed tomographic colonography. Which screening test you choose depends on your risk, your preference, and your doctor. Talk to your doctor about what puts you at risk and what test is best for you.
Chernecky CC, Berger BJ (2013). Laboratory Tests and Diagnostic Procedures, 6th ed. St. Louis: Saunders.
Fischbach FT, Dunning MB III, eds. (2009).
Manual of Laboratory and Diagnostic Tests, 8th ed.
Philadelphia: Lippincott Williams and Wilkins.
Levin B, et al. (2008). Screening and surveillance for
the early detection of colorectal cancer and adenomatous polyps, 2008: A joint
guideline from the American Cancer Society, the U.S. Multi-Society Task Force
on Colorectal Cancer, and the American College of Radiology. CA: A Cancer Journal for Clinicians, 58(3):
Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
U.S. Preventive Services Task Force (2008). Screening for colorectal cancer: U.S. Preventive Services Task Force recommendation statement. Available online: http://www.uspreventiveservicestaskforce.org/uspstf/uspscolo.htm.
How this information was developed to help you make better health decisions.