Skip to content
Blood Test Tracker

Fecal Immunochemical Test (FIT)

A stool test that looks for tiny amounts of blood you cannot see. It is used in routine bowel cancer checks and when bleeding in the gut is suspected.

AI-verified against cited sources. Awaiting expert reviewAlso called FIT, iFOBT, FOBTLOINC 29771-3

What it is

A fecal immunochemical test (FIT) checks a small stool sample for human blood. It uses antibodies that stick to hemoglobin, the protein in red blood cells. It is called an occult (hidden) blood test because the amount of blood is too small to see. You collect the sample at home or in a clinic, and the result is reported as negative or positive. Some labs still use the older guaiac test (gFOBT), which uses a chemical instead of antibodies.

Why it matters

Blood in the stool means there is bleeding somewhere in the digestive tract. Bleeding has many causes and most are not cancer, but polyps and bowel cancers can bleed in ways you cannot see. For adults at average risk, the US Preventive Services Task Force recommends regular colorectal cancer screening from age 45 to 75, and a yearly FIT is one of the recommended options. A FIT is a first step. A positive result usually leads to a colonoscopy.

If it’s high

A positive result means the test found blood in your stool sample. It does not always mean cancer. Your clinician will usually recommend further tests, most often a colonoscopy, to find where the blood is coming from. It is important to follow up even if you feel well.

Common causes

  • Hemorrhoids
  • Blood from menstrual bleeding or the urine getting into the sample
  • Small pouches in the colon wall (diverticulosis)
  • Ulcers or inflammation in the digestive tract, such as ulcerative colitis
  • Polyps, which are growths on the lining of the colon
  • Colorectal cancer

What can help

  • Contact your clinician to talk about next steps, which is usually a colonoscopy
  • Tell your clinician about medicines that can irritate the stomach or bowel, such as aspirin and NSAIDs

What can affect your result

  • Kit type: FIT detects human hemoglobin, while guaiac tests react to substances in food and some medicines
  • Where the bleeding is: hemoglobin from higher in the digestive tract is mostly broken down before it reaches the stool, so FIT mainly picks up bleeding from the lower bowel
  • Other bleeding: menstrual blood, hemorrhoids or blood in the urine can cause a positive result
  • Bleeding that comes and goes: polyps and cancers do not always bleed, so a single negative result does not rule them out
  • Kit and cut-off: each kit has its own detection level (Labcorp's kit detects as little as 100 ng of hemoglobin per mL)
  • Blood from somewhere other than the bowel can cause a positive result, including menstrual bleeding, bleeding hemorrhoids and blood in the urine. Labcorp advises waiting until such bleeding has stopped before collecting the sample.
  • Toilet water or urine mixed into the sample can spoil it. Labcorp says to use the collection paper that comes in the kit.
  • Guaiac (gFOBT) kits can be affected by NSAIDs, vitamin C over 250 mg a day, red meat and some raw fruits and vegetables. FIT kits need no diet or medicine changes (Labcorp, MedlinePlus).
  • Old, overfilled, frozen or wrongly packed samples can be rejected. Labcorp's kit sample is good for 15 days at room temperature.

A FIT only shows whether the sample you collected contained blood. It does not track anything over time.

When to talk to a clinician

If your FIT is positive, contact your clinician soon to arrange follow-up. FIT is meant for people without symptoms, and a negative result can happen even when a bowel problem is present. Tell your clinician about visible blood in your stool, black or tarry stool, a lasting change in bowel habits or weight loss you cannot explain, whatever your FIT result was.

Questions you could ask

  • When is my next bowel cancer check due, and which test is right for me?
  • Do my symptoms or family history change which test I should have?
  • What is the best next step after a positive FIT, and how soon should it happen?
  • Could hemorrhoids, a medicine or menstrual blood have affected this result?

Questions people ask

What is the difference between a FIT and a guaiac test?

A FIT uses antibodies that match human hemoglobin, so food and most medicines do not affect it and no diet changes are needed. Guaiac tests use a chemical that can react to red meat, some raw fruits and vegetables, vitamin C and some medicines. MedlinePlus describes FIT as better at finding blood than the guaiac test.

My FIT was negative. Can I skip my next one?

No. A negative result can happen even when polyps or cancers are present, because they can bleed on and off. That is why FIT is repeated every year when it is used for routine bowel cancer checks. If you have symptoms, tell your clinician even if your FIT was negative.

My FIT was positive. Do I have cancer?

Not necessarily. Blood in the stool has many causes, including hemorrhoids, ulcers and polyps. A positive FIT is a reason to look further, and a colonoscopy is the usual next step.

Show the science and sources

For clinicians and researchers

FIT uses antibodies against the globin portion of undegraded human hemoglobin. Hemoglobin from the upper gastrointestinal tract is mostly digested before it reaches the colon, so the test is relatively specific for lower gastrointestinal bleeding, and it does not react with animal hemoglobin, dietary peroxidases or vitamin C (Labcorp). Guaiac tests detect peroxidase activity of heme and cross-react with diet. Results are usually reported as negative or positive against the kit's cut-off. For example, Labcorp's Polymedco OC-Auto Micro 80 assay detects as little as 100 ng of human hemoglobin per mL, and it needs one stool sample from one bowel movement. Quantitative systems report hemoglobin as mass per volume (LOINC 58453-2 covers this). The 2021 USPSTF recommendation covers adults 45 to 75 (grade A at 50 to 75, grade B at 45 to 49) and selective screening at 76 to 85, and lists annual FIT or high-sensitivity gFOBT, stool DNA-FIT every 1 to 3 years, CT colonography, sigmoidoscopy and colonoscopy as options. The 2017 US Multi-Society Task Force ranks annual FIT and 10-yearly colonoscopy as first-tier tests. A stool DNA-FIT test (Cologuard) is a different test. Labcorp notes that the test is designed for preliminary screening, that a positive result should be followed up with colonoscopy or sigmoidoscopy, and that a negative result can occur in the presence of disease because some polyps and cancers bleed intermittently or not at all.

LOINC 29771-3 (primary), 2335-8, 80372-6. Specimen: stool.

Sources

  1. Occult Blood, Fecal, Immunoassay (ColoFIT) (test 182949), Labcorp
  2. Fecal Occult Blood Test (FOBT), MedlinePlus Medical Tests (National Library of Medicine)
  3. Colorectal Cancer: Screening (final recommendation statement), US Preventive Services Task Force (2021)
  4. 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)
  5. Colorectal Cancer Screening: Recommendations for Physicians and Patients from the U.S. Multi-Society Task Force on Colorectal Cancer, American Journal of Gastroenterology (2017)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

Related markers