Colon Cancer Risk Test: An Overview of Screening, Diagnostic, and Genetic Tests for Colon Cancer

Colon Cancer Risk Test: An Overview of Screening, Diagnostic, and Genetic Tests for Colon Cancer
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What is Colorectal Cancer Screening?

Doctors use many types of tests to evaluate a person’s risk for certain cancers, like colon cancers. Screening tests are one such colon cancer risk test option. Diagnostic tests are another.

Screening tests for colon cancer are a proactive method of detecting and removing precancerous polyps, as well as looking for developing cancers in the rectum and colon. Why is screening so important? According to the experts at the Fox Chase Cancer Center (FCCC), “Studies show that screening for colorectal cancer helps decrease the number of deaths from the disease.” (1)

Here we examine the five screening tests currently used, which are:

  1. Fecal occult blood test
  2. Sigmoidoscopy
  3. Barium enema
  4. Colonoscopy
  5. Digital rectal exam

According to Cedars-Sinai Colorectal Cancer Center, “Most colon and rectal cancers are discovered through either a colonscopy or barium enema.” (2)

Later, we will briefly explore some pending screening tests, which are currently in clinical trials, such as a virtual colonoscopy and the DNA stool test, as well as some diagnostic tests used for the staging of colon cancer patients.

Fecal Testing Options

Your doctor will recommend one of three types of testing kits: a fecal occult blood test kit (FOBT), a fecal immunochemical test (FIT,) or a flushable reagent stool blood testing kit. These tests can be done in the privacy of your home; they are easy to perform and painless.

The fecal occult blood test involves collecting several stool samples for microscopic analysis of any traces of human hemoglobin (blood.) If blood is detected, it could signal the presence of polyps or cancer. Individuals should be aware that according to information from Harvard Health Publications, FOBT is considered less effective than colonoscopy or sigmoidoscopy in detecting cancer.

Positive FOBT

The testing is simple and painless. Typically, individuals collect three stool samples on three different days, and put the samples on special chemically treated cards. The cards are returned to the doctor for analysis. The only special preparations needed are to abstain from taking NSAIDs or blood thinners for a few days prior to the test. Your physician will tell you how many days of abstinence are needed. Other than that, individuals with hemorrhoids should make sure that the hemorrhoids are not bleeding, and women should not be menstruating. There are no risks associated with this screening method. The FIT test is very similar, but offers the benefit of freeing individuals from dietary and drug restrictions, as these do not affect test results.

The test results are usually available within one week. If blood is detected by testing, your physician may recommend other types of tests to rule out possible diseases.

If your doctor recommends a flushable reagent stool blood test, it can be obtained at any pharmacy. The benefit of this test method is individuals do not have to touch the stool sample, and the pads are simply flushed away after the test.

What is a Flexible Sigmoidoscopy?

For this colon cancer screening test, the doctor or gastroenterologist examines an individual’s lower intestine using a sigmoidoscope. This test detects cancers and polyps.

Your doctor may recommend some or all the following for preparation:

  • Liquid diet the night before
  • Enemas prior to the test
  • Laxative the night before
  • Avoid NSAIDs or blood thinners for a specific period prior to the test

Individuals with diabetes may receive special instructions from their physicians to help them avoid any complications from the testing. Other than the risk to diabetics, there are minimal chances of perforation or bleeding.

You will know the preliminary results immediately, but if the doctor had to take any biopsies of suspicious tissues, it takes a few days for the laboratory to issue a report. If the doctor finds any polyps or cancer, he may recommend a colonoscopy.

What is a Double Contrast Barium Enema (DCBE)?

To take an x-ray of the rectum and colon, it is necessary to inject barium sulfate and air into an individual’s rectum to make those areas visible. This type of screening test detects colon cancer and polyps, and may also be referred to as an air-contrast barium enema or a barium enema with air contrast.

Intestinal polyposis (Peutz-Jegher syndrome) Barium Enema

Intestinal Polyposis (Peutz-Jegher syndrome) Revealed by Barium Enema

Your physician may have you do some or all the following prior to a barium enema:

  • Eat a light breakfast the day prior
  • Eat a liquid lunch and liquid dinner the evening before the test
  • Drink clear liquids
  • Avoid dairy products
  • Take a laxative
  • Skip breakfast the day of the test
  • Avoid medications like NSAIDs or blood thinners

While there are no common risks associated with a barium enema, individuals that are pregnant or diabetic should consult their doctor for any special instructions. Typically, test results are available within a couple of business days.


This test allows the gastroenterologist or endoscopist to examine the length of the large intestine - from the rectum to the opening of the small intestine - for cancer.


The preparation for a colonscopy is detailed and time-consuming, so it is important to follow your doctor’s instructions completely to make sure the colon is properly emptied prior to the test. Preparations typically start five days prior to the procedure, and include, but are not limited to:

  • Avoiding solid foods the day prior to the test, and drinking only clear liquids
  • Ingesting a strong laxative or other bowel-cleansing substance

Note: the side effect of any bowel-cleansing substance used to prepare for a colonoscopy is severe diarrhea. Individuals should be aware of this possibility.

The population of patients that may need special consideration when undergoing a colonoscopy are those with: kidney disease, diabetes, congenital heart disease, mitral value replacement, or on dialysis.

Some risks associated with a colonoscopy are:

  • Bleeding
  • Perforation of the colon
  • Breathing problems
  • Irregular heartbeat

Colonoscopy is considered the best cancer screening test, according to information from NetWellness, because “colonoscopy is the best method that has a high sensitivity for all polyps, both small and large, and which presents the capability of removing them at the time of the procedure.” (3) The American Cancer Society also supports the use of colonoscopy for early detection of colon cancer.

Genetic Screening Tests for Familial Colon Cancer

While not part of the five screening tests commonly used for early detection of colon cancer, genetic tests are available for individuals at risk for heritable colon cancer. These are done by drawing blood, and test for the following:

  • Familial adenomatous polyposis (FAP)
  • Hereditary non-polyposis colorectal cancer (HNPCC), which is also referred to as Lynch Syndrome
  • MYP polyposis
  • Juvenile polyposis
  • Peutz-Jeghers
  • Cowden’s

Individuals with a family history of polyps, colon, or other gastrointestinal cancers should consult with their physician regarding the advantages of genetic screening tests.

Diagnostic Screening Tests for Colon Cancer

Diagnostic tests for colon cancers are used to determine the severity, which is called the stage, of the spread of colorectal cancer in an individual’s body. These tests aid doctors in diagnosing, staging, and treating these cancers.

Let’s talk about the most common diagnostic tests for colon cancers: PET/CT scans and transrectal ultrasounds.

While a computerized tomography (CT) scan and a positron emission tomography scan (PET) may be performed separately, many experts, like those at the University of Colorado Hospital believe they are most effective when performed in conjunction with each other. In their words, “PET/CT is approximately 90% accurate in detecting many of these cancer types.” (like colon cancer.) How do they work?

CT Scan Equipment

CT Scan

A CT scan provides highly detailed x-rays of cross-sections of the body, such as the abdomen and pelvis. The PET scan uses radionuclides to pinpoint biological body functions, such as the metabolic activity of cancer cells, and identifies the cancerous mass.

A transrectal ultrasound is performed by inserting a probe into the rectum and using soundwaves to take pictures of the inside of it.

Future Screening Methods for Colon Cancer

There are screening methods currently in clinical trials that may provide improved methods for diagnosing polyps and colon cancers that are non-invasive and safe for individuals. Two of these are: CT colonography (virtual colonoscopy), and DNA-Based stool test.

A virtual colonoscopy builds on the images provided by a conventional CT scan, which are two-dimensional, by providing three- dimensional pictures as well.

DNA stool tests are used to identify DNA information from cancer cells, rather than hidden blood, in fecal samples.

No matter what colon cancer risk test your physician may recommend, it is important to follow his advice and have the test. Early detection and intervention with the appropriate colon cancer treatment is critical. According to the American Cancer Society, “Regular screening can often find colorectal cancer early, when it is most likely to be curable. In many cases, screening can also prevent colorectal cancer altogether.” (4) Why take a risk, when this type of cancer is easily prevented and detected?

Reference Sources

1. Fox Chase Cancer Center, “Colorectal Cancer Screening,” accessed 09/03/2010

2. Cedars-Sinai, “Cancer Diagnosis,” accessed 09/03/2010

3. NetWellness Consumer Health Information, “Colorectal Cancer,” accessed 09/03/2010

4. American Cancer Society, “Can colorectal polyps and cancer be found early?”

Harvard Health Publications, “Fecal Occult Blood Test,” accessed 09/03/2010

Harvard Health Publications, “Diagnostic Tests - Flexible Sigmoidoscopy,” accessed 09/03/2010

Harvard Health Publications, “Diagnostic Tests - Barium Enema,” accessed 09/03/2010

Penn Medicine, Division of Gastroentrology, “Heritable Colon Cancer Syndromes,” accessed 09/03/2010

University of Colorado Hospital, Imaging Services

American Cancer Society

Image Credit

Colonoscopia/Wikimedia Commons/Public Domain

Positive FOBT/Wikimedia Commons/Jmh649/Creative Commons Attribution ShareAlike 3.0 Unported License

Intestinal Polyposis/Wikimedia Commons/robhengxr/Creative Commons Attribution 2.0 Generic License

CT Scan/Wikimedia Commons/Public Domain