Fecal Immunochemical Test to Detect Hidden Blood

A fecal immunochemical test (FIT)—also called an immunochemical fecal occult blood test, or FOBT—is used to test the stool for blood that can not be seen with the naked eye (called occult blood). A FIT is often used to detect bleeding in the digestive tract when there are no other signs or symptoms of a digestive problem. Blood in the stool can be caused by a number of conditions, including cancers of the digestive tract such as colon cancer.

If your doctor ordered this test, follow the instructions you were given. The good news is that it's a really easy test to take, and it doesn't require that you prepare in any way. Try not to worry about why your doctor ordered the test; see what the results are first and what your doctor thinks is going on before you start to think the worst.

Blood tests for thyroid disease, including TSH, Free T4, Free T3, antibodies
David Silverman / Getty Images

How Is a FIT Different Than a FOBT?

A FIT is similar to the FOBT, except that the FIT doesn't require patients to follow a restricted diet before taking the test. To take a FOBT, patients must not eat any red meat and also must stop taking certain medications for a number of days prior to the test. A FIT may not be able to detect blood from further up the digestive tract, such as in the stomach. This means that it is more specific to finding blood coming from the lower gastrointestinal tract than the FOBT. Many patients also find the collection methods of the FIT easier than those of the FOBT.

Why FIT Is Used

Fecal occult blood tests such as the FIT or the FOBT are usually recommended at regular intervals to screen for colon cancer starting at age 50 and continuing until age 75. People at high risk for colon cancer because of family history or polyps may begin testing earlier, as determined by a physician. (The American Cancer Society recommends getting tested as early as age 45.)

Preparation

The FIT doesn't require any special preparation, but there are some conditions that could affect the results. You should not use the FIT if you:

  • Have active bleeding from hemorrhoid or anal fissure
  • Have blood in your urine
  • Are a woman having a menstrual period or are within three days after the end of your period

Collecting Samples

You will be given a kit to be used for collecting stool samples for the test. This kit should be kept in the bathroom at home, or carried with you when you're away from home during the test. Be sure to write your name and other information on the collection cards.

Flush the toilet before a bowel movement. After having a bowel movement, don't flush right away! Instead, brush the surface of the stool with one of the brushes from the kit for several seconds. Shake the brush once to dislodge any clumps of stool or excess water. Apply the sample by swabbing the appropriate spot on the test card for several seconds with the bristles of the brush. Dispose of the brush as directed by the instructions included with the kit.

Repeat the process for one more bowel movement or as directed by your doctor. Cover the test cards and store them away from heat, light, and strong chemicals.

After finishing the test, seal the test envelope and return the kit to your doctor or the laboratory.

Risks

This test is safe and painless.

Following up After the Test

Call your doctor in a few days for the results. If the test shows that there is blood in the stool (a positive test), don't panic. There are many reasons blood could be in your stool. Your doctor will likely want to do more tests to find out why the blood is there. In some cases, another test called a colonoscopy may be recommended.

If the test is negative (shows no blood in the stool), find out what your doctor wants you to do next, if anything, and if the test should be repeated after a period of time (such as 1 year or 5 years).

When You Should Call the Doctor

If you have diarrhea or constipation during the test period.

Other Important Information

Read all instructions that come with the kit carefully before testing begins.

Was this page helpful?
Article Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. American Cancer Society. Colorectal cancer screening tests. Updated May 30, 2018.

  2. National Institute of Diabetes and Digestive and Kidney Diseases. Symptoms and causes of GI bleeding. Updated July 2016.

  3. Centers for Disease Control and Prevention. Colorectal (colon) cancer: What should I know about screening? Updated January 30, 2019.

  4. American Cancer Society. Colorectal cancer screening guidelines. 2018.

  5. Robertson DJ, Lee JK, Boland CR, et al. Recommendations on fecal immunochemical testing to screen for colorectal neoplasia: a consensus statement by the US Multi-Society Task Force on Colorectal Cancer. Gastroenterology. 2017;152(5):1217-1237.e3. doi:10.1053/j.gastro.2016.08.053

Additional Reading