December 28, 2022
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What is a fecal immunochemical test (FIT)?

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A fecal immunochemical test (FIT) is a screening test for bowel cancer. This test checks for hidden blood in the stool, which can be a sign of bowel cancer. FIT tests are increasingly used to screen for bowel cancer because they can be conducted from home and are less invasive than a colonoscopy. If the result of the FIT is positive, further investigation such as a colonoscopy can be scheduled. Detecting bowel cancer early provides the greatest chance for a cure.

What is an FIT?

The abbreviation FIT stands for fecal immunochemical test. This test checks for traces of human blood in stool that are too small to see (MedlinePlus). Blood in stool can be a sign of several medical conditions, including bowel cancer. A positive test result means that blood was detected in the stool sample.

Reference values FIT:

< 50 ng/ml: negative

≥ 50 ng/ml: positive

What is occult blood?

Occult blood is blood that cannot be seen with the naked eye. A FIT checks for occult blood in the stool. Bowel polyps and cancers can bleed into the digestive tract, causing blood to appear in the stool (Mayo Clinic, 2022). In early stages, the amount of blood is usually so small it can only be detected with a test.

Why are FITs important?

Bowel cancer is highly treatable in its early stages, which is why catching it early is important. Additionally, bowel cancer often has little to no symptoms in the beginning, meaning screening tests are needed to help detect it (Mayo Clinic, 2022). FITs are a non-invasive, accessible way to screen for bowel cancer. In addition to catching bowel cancer earlier, stool testing can allow pre-cancerous polyps to be detected and removed before they become cancerous.

Risks of FITs

FITs are relatively low-risk as they only require a stool sample. However, no screening test is perfect and it is possible that a polyp or cancer is missed if it is not bleeding at the time of the test (Mayo Clinic, 2022). That is why it is recommended to repeat the FIT regularly. 

It is also possible that the FIT will detect bleeding from polyps that are not cancerous This means having to go through the process of a colonoscopy and polyp removal with no benefit to your health (NIH, 2022). In older adults, the FIT may detect cancers that would not shorten an individual’s lifespan. This can result in unpleasant surgery and treatment for cancer that would not lengthen an individual’s life (NIH, 2022). The recommended ages for colon cancer screening were created to balance the risks of the test with the benefits. This is why the screening age group is approximately 50-55 to 75 years old. 

Who is a fecal occult blood test for?

A fecal occult blood test is intended for people who meet the requirements for colon cancer screening and are of average risk. Average risk means individuals within the screening age group with no family history of bowel cancer, no personal history of bowel polyps, and no inflammatory bowel diseases (American Cancer Society, 2020). The screening age group varies by country, but is usually between 50-55 and 74. 

Individuals may choose to do a FIT at a younger age if they have certain factors that increase their risk of developing bowel cancer. If you have a family history of bowel cancer, genetic disorders that predispose you to bowel cancer, certain inflammatory bowel diseases, or a personal history of bowel polyps, speak to your doctor. You may require a colonoscopy rather than an FIT (American Cancer Society, 2020). If you have symptoms of bowel cancer, this test is also not recommended. Proceed directly to your GP. 

How does an FIT work?

An FIT is easy to perform from home. The test kit contains everything you need to perform the test. This test requires you to take a stool sample and send it to a laboratory by mail for analysis.

Causes of fecal occult blood

Blood in the stool can occur for several reasons, and is often not related to bowel cancer. However, if your FIT is positive, more investigation is needed to rule out cancer. Other causes of blood in the stool are:

  • Crohn’s and ulcerative colitis
  • Hemorrhoids
  • Bleeding in gastrointestinal tract
  • Bowel polyps
  • Irritation of the stomach or esophagus
  • Anal fissures
  • Ulcers
  • Intestinal infections

Source: Ambardekar, 2020

What should I do if my test result is positive?

If your FIT is positive for occult blood, see your GP. A positive test result does not necessarily mean you have bowel cancer, but more investigation is needed to find the course of the bleeding. You will likely be referred for a colonoscopy to check for polyps or abnormalities in the colon or rectum.

References

Ambardekar, N. (2020, September 1). The Basics of Fecal Occult Blood Tests. WebMD. https://www.webmd.com/colorectal-cancer/guide/fecal-occult-blood-test

Colon cancer – Symptoms and causes. (2022, October 8). Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/colon-cancer/symptoms-causes/syc-20353669

Colorectal Cancer Guideline | How Often to Have Screening Tests. (n.d.). https://www.cancer.org/cancer/colon-rectal-cancer/detection-diagnosis-staging/acs-recommendations.html

Fecal immunochemical test (FIT). (n.d.). https://medlineplus.gov/ency/patientinstructions/000704.htm

Fecal occult blood test – Mayo Clinic. (2022, May 4). https://www.mayoclinic.org/tests-procedures/fecal-occult-blood-test/about/pac-20394112

National Institutes of Health. (2022, June 10). Colorectal Cancer Screening (PDQ®)–Patient Version. National Cancer Institute. https://www.cancer.gov/types/colorectal/patient/colorectal-screening-pdq

About the author

Lauren Dobischok

Lauren is a health scientist and science communicator living in the Netherlands. With a background in epidemiology, her goal is to create accurate scientific content that is easy to understand and empowers people to make informed decisions. Her favourite topics to discuss are public health, infectious diseases, and dispelling myths and misconceptions about health topics with research. Coming from Canada, Lauren prefers to spend her free time learning Dutch and exploring the interesting sights this small country has to offer!