Colorectal Cancer Screening Facts You Should Know

Colonoscopy or other colon cancer screenings are important routine tests

/ Author:  / Reviewed by: Joseph V. Madia, MD Beth Bolt, RPh

It's probably safe to say that few people look forward to a colonoscopy. But knowing how much colonoscopy and other colorectal cancer screening cuts cancer risk may be enough for most people to get screened.

Since it can take years for abnormal growths called polyps to become cancerous, colorectal cancer screening can detect abnormal tissue early. Early detection allows pre-cancerous polyps to be removed, and spotting cancer early leads to greater chances of successful treatment.

When do you need a colorectal cancer test?

The American Cancer Society (ACS) recommends that, beginning at age 50, most people have one of the following screening tests.

  • Sigmoidoscopy every five years
  • Colonoscopy every 10 years
  • Double-contrast barium enema every five years
  • Virtual colonoscopy every five years

If abnormal tissue is detected during these procedures, your doctor will recommend testing at shorter intervals.

Who needs these tests more often?

People with a higher than average risk for colorectal cancer need more frequent colon screening tests. According to the ACS, these people include those with:

  • A personal history of colorectal cancer or polyps
  • A personal history of inflammatory bowel disease (ulcerative colitis or Crohn's disease)
  • A strong family history of colorectal cancer or polyps
  • A known family history of a hereditary colorectal cancer syndrome, such as familial adenomatous polyposis (FAP) or hereditary non-polyposis colon cancer (HNPCC)

Preparing for colon screening tests

The goal of prepping for any colon tests is to clear your intestines of all solid material. You doctor will give you specific instructions for how to do this. The voiding process may include enemas or laxatives after you stop eating solid foods one to three days before the test.

Clear liquids will be allowed during the days your doctor requests that you do not eat solid foods.

MedlinePlus lists these examples of allowable clear liquids:

  • Clean coffee or tea
  • Fat-free bouillon or broth
  • Gelatin
  • Sports drinks
  • Strained fruit juices
  • Water

Laxatives may be in the form of medication that stimulates a bowel movement or a liquid consisting of magnesium citrate that is consumed with lots of water. In an enema, liquid is injected into the rectum to force bowel movements that empty all the contents of the intestines.

Carolyn Dean, MD, ND, Medical Advisory Board Member of the non-profit Nutritional Magnesium Association, told dailyRx News that she asks her patients to use the magnesium citrate bowel prep, not a chemical prep.

"The dosage for a magnesium citrate prep is about 30 grams. The RDA [recommended daily allowance] for magnesium is about 400 mg. Such high amounts of magnesium will cause a strong laxative effect, flushing out most of the magnesium," Dr. Dean said.

"Some people say they actually feel better after a colonoscopy. That may be due to the relief that their colon is healthy. Or it can be because they absorbed some of the magnesium, which gives them energy and relaxed muscles and improved sleep. If that's the case, think about continuing to take some magnesium every day, but at a much lower dosage of magnesium citrate powder made into a tea or a refreshing drink," Dr. Dean recommended.

Virtual colonoscopy

In this test, you will lie on your left side while a small flexible tube is inserted into the rectum and air is pumped through to expand the colon. After this step, you will lie on your back and x-rays will be taken of your colon in a CT machine. This test is usually done as a follow-up test if you’ve had colorectal cancer, but can be done as a routine screening test.

The benefits of this test are that you won’t need sedatives and no scope will be inserted into your colon. The disadvantage is that, if your doctor sees polyps or suspicious areas, a biopsy cannot be taken during this procedure and a colonoscopy will be needed.


In sigmoidoscopy, a flexible tube containing a scope is placed through the anus and gently moved into the colon. Air is blown into the intestines so that the doctor can see the inside of the intestines more clearly.

Because you will not be sedated for this test, you will likely feel the pressure of the scope in your intestines. It may give you the feeling of needing to have a bowel movement. If the doctor sees any polyps or other areas of concern, a biopsy can be taken with an instrument passed up through the scope.

Some patients find a sigmoidoscopy is easier than colonoscopy because they are not sedated and there may not be as many days of dietary restrictions before sigmoidoscopy as before colonoscopy. A sigmoidoscopy, however, only looks at the left side of the colon and may not detect problems in other parts of the colon.

There is a very slight risk of bleeding caused by the procedure or from the removal of biopsy material.

After the exam, you will pass the air that was blown into your colon.


Before colonoscopy, you’ll likely be given sedating medication through an IV. You will not feel or be aware of the procedure and won’t remember it when it is done. During the procedure, a scope in inserted through the anus and moved up into the large bowel.

Air will be blown through the scope to expand the bowel. The doctor looks at the bowel as the scope is moved out of the bowel. A colonoscopy allows the doctor to see the entire colon. Any polyps or other areas of concern can be removed during the procedure with forceps inserted through the scope.

There are risks associated with the colonoscopy procedure that include risk of infection and bleeding from a tear or site of a biopsy.

Cramping and gas is not uncommon after a colonoscopy. Because you’ve been sedated, you will need a ride home.

Speaking about the benefit of colonoscopies, Dr. Dean commented, "Colonoscopy is a very useful screening tool and I do recommend it. I tell my telephone consulting clients to be sure and go to a screening center where they specialize in colonoscopy, making them experts with a low rate of side effects."

Dr. Dean went on to explain that since research has shown "that a higher magnesium intake seems to be associated with a modest reduction in the risk of CRC [colorectal cancer], in particular, colon cancer, [it] is an important reminder of the importance of this mineral. Magnesium assists the liver's detoxification pathways, acts as a gentle laxative both by drawing fluid into the bowel by osmosis and by relaxing tight intestinal muscles. Dumping toxins quickly and efficiently from the colon is an important aspect of colon cancer prevention."

Double-contrast barium enema

This test involves a series of x-rays taken of the colon and rectum after the patient is given an enema with a barium solution. The patient is not sedated for this procedure.

This test is not as sensitive as a colonoscopy for detecting cancer, but it is useful for people who cannot have a colonoscopy, such as the elderly and bedridden people.

This procedure can be used to find polyps in your colon and is also useful in diagnosing diverticulitis (inflamed or infected colon) and inflammatory bowel disease, such as Crohn's disease or colitis.

Review Date: 
April 28, 2014
Last Updated:
May 7, 2014