What Tests Are Used to Diagnose Colon Cancer?

Learn the Basics About Colon Cancer Diagnosis

Mature female patient in exam room with doctor. Credit: Thomas Barwick / Getty Images

A person with colon cancer will be diagnosed in one of two ways:

  1. It is found on a routine screening test.
  2. Symptoms lead a person to the doctor, and tests to find the cause of the symptoms reveal colon cancer.

Ideally, every case of colon cancer would be found with routine screening. This is because in the early stages, people with colon cancer typically have no symptoms at all, and colon cancer is most curable when found early, at the time it’s least likely to cause symptoms.

Even better is when a routine screening identifies polyps or adenomas. If these growths in the colon are left untreated, they may develop into colon cancer. In cases where they’re caught early, the growth can be removed before it even has a chance to turn into cancer.

What Tests Are Used to Diagnose Colon Cancer?

There are several different tests to look for colon cancer, and each test has pros and cons. If you’re over age 50, routine colon cancer screenings should be part of your stay-healthy plan.

Tests that are used to make a colon cancer diagnosis include:

  • Flexible sigmoidoscopy
  • Colonoscopy

Tests that can identify the possibility of colon cancer include:

  • Double-contrast barium enema (DCBE)
  • Fecal occult blood test (FOBT)
  • CT colonography or virtual colonoscopy
  • Fecal immunochemical test
  • Stool DNA tests

The double contrast barium enema and fecal occult blood test are common and will likely be options for you if you are seeking colon cancer testing.

The CT colonography, fecal immunochemical test, and stool DNA tests are newer and may not be options for everyone. Many insurance plans won’t cover these tests and not all health care facilities and offices offer them.

What are the Pros and Cons of Different Colon Cancer Diagnosis Tests?

Flexible sigmoidoscopy and colonoscopy are more invasive than other tests, but only these two tests can identify colon cancer without the need for more tests.

The other five tests are less invasive, but they only tell you that colon cancer may be present. Then you need to follow up with a sigmoidoscopy or colonoscopy to get a final diagnosis.

You may wonder, "If I end up needing a sigmoidoscopy or colonoscopy anyway, why bother with these other tests?"

Mainly, the double contrast barium enema (DCBE), CT colonography, fecal occult blood test (FOBT), fecal immunochemical test, and stool DNA tests are useful because they help doctors decide who might need further testing. If these tests come back showing no hint of colon cancer (negative), you may be able to avoid the more invasive sigmoidoscopy or colonoscopy tests.

  • What is a Colonoscopy?
  • Information on the colonoscopy test, including how to prepare for it, what happens during the test, and possible complications of the test.
  • What is a Double Contrast Barium Enema (DCBE)?
  • Information on the double contrast barium enema (DCBE) test, including how to prepare for it, what happens during the test, and possible complications of the test.
  • What is a Fecal Occult Blood Test (FOBT)?
  • Information on the fecal occult blood test, including how to prepare for it, how the test is completed, and how to follow up if you have positive results on the FOBT.


Halpern MT, Pavluck AL, Ko CY, Ward EM. Factors Associated with Colon Cancer Stage at Diagnosis. Dig Dis Sci 2009 Jan 1. [Epub ahead of print].

MDLinx Oncology. Colon Cancer Blood Test

Medline Plus.

Colorectal Cancer

The American Cancer Society. After Diagnosis: Staging Colon and Rectum Cancer

The American Cancer Society: Learn About Colon and Rectum Cancer. 

The American Cancer Society. Should I Be Tested for Colon and Rectum Cancer? 

The National Cancer Institute: Colon and Rectal Cancer