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Stool Tests for Colorectal Cancer

How It Feels

You may find it unpleasant to collect a stool sample for these tests.

Risks

These tests do not have any risks.

Results

For some FOBT kits, you can read the results yourself. Other tests, including FIT/iFOBT and stool DNA, are read by your doctor.

Stool tests
Normal:

A normal FIT/iFOBT or FOBT test means that there was no blood in your stool at the time of the test. A normal sDNA test means that no abnormal cells were found. Normal test results are called negative.

Abnormal:

An abnormal FIT/iFOBT or FOBT test means that there was some blood in your stool at the time of the test. An abnormal sDNA test means that some abnormal cells were found. Abnormal test results are called positive.

Normal results

If a stool test is normal, it does not always mean colorectal cancer or colon polyps are not present. That's because these tests can miss polyps and some cancers.

Talk with your doctor about how often you should do a test, depending on your age and any risk factors you may have for colorectal cancer.

Abnormal results

A colon polyp, a precancerous polyp, or cancer can cause a positive stool test. With a positive test, there is a small chance that you have early-stage colorectal cancer.

Talk with your doctor about what test you may need next. Most of the time, an abnormal stool test means that you will need to have a colonoscopy.

What Affects the Test

Reasons you may not be able to have a stool test or why the results may not be helpful include:

  • Having blood in the urine, menstrual bleeding, hemorrhoids, an anal fissure, bleeding gums, or nosebleeds.
  • Having cleaning products in the toilet water at the time of the test.

What To Think About

  • Stool tests can produce false-positive and false-negative results.
    • False-positive means that the test may be positive when you don't have a polyp or cancer.
    • False-negative means that the test may be negative when you do have a polyp or cancer.
  • These tests may miss polyps and some cancers.
  • The stool DNA test is still new, and it isn't available everywhere.

WebMD Medical Reference from Healthwise

Last Updated: October 30, 2013
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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