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Stool Tests for Colorectal Cancer

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Colon Cancer: Which Screening Test Should I Have?

Why It Is Done

Stool tests are done:

  • To look for signs of cancer.
    • FOBT and FIT/iFOBT tests look for blood in the stool. These tests are useful to screen for colon cancer, because tissue or polyps with cancer are more likely to bleed than normal colon tissue. If bleeding is found, more tests will be done to find the cause. It's important to call your doctor if a home test shows blood in your stool. A home test doesn't replace the need for a regular exam by your doctor.
    • Stool DNA tests look for abnormal changes. Colon cancer cells often contain DNA changes in genes. Cells with these changes can be shed into the stool, where this test may be able to find them.
  • To help find the cause of abdominal pain.
  • To check for the cause of anemia.
  • As part of a routine physical exam for those with a higher chance of getting colorectal cancer, especially at age 50 and older.

How To Prepare

Since colorectal cancers do not bleed all the time, FOBT and FIT/iFOBT tests are done over several days on different stool samples. This increases the chance of finding blood in your stool if it exists. A stool DNA test requires only one sample.

You may need to avoid certain foods for 2 to 3 days before the test. This depends on what kind of stool test you use. If you aren't sure, ask your doctor.

Do not do the stool tests during your menstrual period or if you have active bleeding from hemorrhoids. Also, do not test a stool sample that has been in contact with toilet bowl cleaning products that turn the water blue.

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?).

How It Is Done


You will need to collect stool samples over three different bowel movements on three different days. The test kit includes a wooden applicator and test cards. Be sure to follow the instructions that come with your test kit, including any instructions to avoid certain foods in the days before the test.

  • Complete the identification information on the front of each card.
  • During a bowel movement, collect a small amount of stool on one end of an applicator. You might try catching the stool on some plastic wrap draped loosely over the toilet bowl and held in place by the toilet seat. If you use a container to collect the stool, first clean and rinse it well to get rid of any substance that may affect the test results.
  • Apply a thin smear of stool inside box A.
  • Reuse the same applicator to obtain a second sample from a different part of the stool. Apply a thin smear inside box B.
  • Close the cover of the slide.
  • The next two times you test your stool, complete the remaining cards in the same way.
  • Return all slides to your doctor either in person or by mail within 4 days of collecting the samples.
  • If your test kit has the developer solution, wait 3 to 5 minutes before you put 1 drop of the developer solution on the area with the stool. Put 1 drop of the developer solution on the control areas of the card so that you will know what positive and negative test results should look like. An area to read the results is found on the reverse side of the card. Turn the card over and read the results within 10 seconds.

WebMD Medical Reference from Healthwise

Last Updated: January 17, 2012
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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