Fecal occult blood test (FOBT/FIT)
Stool test for blood you cannot see, used among other things to detect colorectal cancer early
Also known as
Definition
The fecal occult blood test looks for blood that cannot be seen with the naked eye. Blood in the stool means there is bleeding somewhere in the digestive tract. There are two main methods: the guaiac test (gFOBT), which detects blood chemically, and the immunochemical test (iFOBT or FIT), which detects hemoglobin with antibodies and is considered better at finding blood in the stool. The test alone does not make a diagnosis.
| Parameter | Value |
|---|---|
| Unit | Result usually reported as detected (positive) or not detected (negative) |
| Reference Range | Typical unremarkable result in adults: no blood detected in the stool (negative). Test methods and labs differ; the assessment on your own report is what counts. Discuss the result with your doctor. |
Agree on your personal target range with your doctor.
↓ What a low value means
A negative result means that no blood was found in the samples tested. It does not reliably rule out a bowel condition: as with other colorectal cancer screening tests, false negative results are possible, meaning normal results even though colorectal cancer is present. When the stool test is used as a screening method, it is repeated regularly, every year according to US recommendations. If you have ongoing symptoms, discuss next steps with your doctor, even if the test was normal.
↑ What a high value means
A positive result means there is likely bleeding somewhere in the digestive tract. Possible causes include polyps, hemorrhoids, diverticula, ulcers, ulcerative colitis or benign tumors; colorectal cancer can also be behind it. So a positive result does not automatically mean cancer, and false positive results do occur. To find the location and cause of the bleeding, further tests usually follow, most commonly a colonoscopy. Your doctor decides what makes sense in your case.
When to test
Mainly as a screening test for colorectal cancer in people without symptoms; discuss with your doctor at what age and how often. Also when there are signs of bleeding in the digestive tract, when looking for the cause of anemia, and to help tell irritable bowel syndrome apart from inflammatory bowel disease. You usually collect the samples at home following the kit instructions; with the guaiac test, no urine should get into the sample.
Frequently asked questions
What is the difference between the guaiac test and the immunochemical test? +
The guaiac test (gFOBT) detects blood with a chemical and usually needs samples from two or three separate bowel movements. The immunochemical test (iFOBT, FIT) detects hemoglobin with antibodies, needs samples from one to three bowel movements depending on the brand, and is considered better at finding blood in the stool.
Do I need to prepare for the test? +
For many tests, no. With some guaiac tests, foods, supplements and medicines can affect the result, for example red meat, certain raw fruits and vegetables, vitamin C in amounts over 250 mg a day, and nonsteroidal anti-inflammatory drugs such as ibuprofen, naproxen or aspirin. Your doctor will tell you what to avoid and for how long; do not stop prescribed medicines on your own.
Does a positive test mean colorectal cancer? +
No, not automatically. A positive result shows blood in the stool, which can have many causes, such as hemorrhoids, polyps or ulcers. False positive results are also possible. The test alone cannot diagnose a condition; a colonoscopy usually follows to find the cause.
Does a stool test replace a colonoscopy? +
The stool test is one of several screening methods for colorectal cancer, alongside the stool DNA test, colonoscopy, sigmoidoscopy and CT colonography. Each method has pros and cons. After a positive stool test, colonoscopy is the most common follow-up test. Discuss with your doctor which method suits you.
Fecal occult blood test (FOBT/FIT)
Sources
Last updated: October 05, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.