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Fecal occult blood test
Screening for hidden gastrointestinal bleeding. A key colon cancer prevention test — no diet needed with the immunochemical method.
Other names: FIT, guaiac testSection: GI tractSpecialist: Gastroenterologist, primary care physicianSample: Stool
Updated: September 17, 2026·MedProtect editorial team Reference information — not a diagnosis or a prescription
In shortNormal — no occult blood is found in stool. The modern immunochemical test (FIT) requires no diet or medication withdrawal. A positive result is a reason to see a doctor: causes range from hemorrhoids and fissures to polyps and colon cancer; in screening, colonoscopy follows.
What this marker is
Small bleeding from the stomach or intestines is invisible to the eye, but the test catches traces of blood in stool. Two methods exist: the older guaiac test — requiring 3 days without meat, fish and iron — and the modern immunochemical test (FIT), which reacts only to human hemoglobin and needs no preparation.
The test is part of colon cancer screening programs for people aged 50–75: regular testing lowers mortality because polyps and early tumors bleed long before symptoms appear.
Reference ranges
Group
Reference range
Normal
no occult blood found (negative)
Immunochemical test (FIT)
the cutoff is usually 10–20 µg Hb/g of stool — per the lab report
Positive
requires a doctor’s review: from benign causes to colonoscopy
A single negative result does not fully exclude a source: bleeding can be intermittent, so screening is repeated every year or two. Blood visible to the eye is a reason to see a doctor regardless of the test. Ranges differ between laboratories.
Check your value
Enter the number from your lab report — see how it compares with the typical range. Mind the units shown in the chosen row.
An approximate comparison with a typical range, not a diagnosis. Ranges differ between laboratories — use the one on your report; a doctor interprets the result.
When it is high or appears: possible causes
Hemorrhoids and anal fissuresThe most common benign causes — blood from the lower tract.
Colon polypsBleed without symptoms — the main screening target.
Colon cancerEarly stages often show only occult blood.
Stomach and intestinal ulcersBleeding erosions and ulcers of the upper tract.
IBD and diverticulaInflammatory bowel disease and diverticulosis.
NSAIDsLong-term ibuprofen-like drugs irritate the GI lining.
What can skew the result
These factors can shift the result without any disease — keep them in mind before a retest:
Guaiac method: meat, fish, iron distort itBleeding gums or noseMenstruation — better to postponeFIT needs no diet
How to prepare
For the immunochemical test (FIT) no preparation is needed: no diet, no medication changes. For the guaiac test — 3 days without meat, fish, iron supplements and vitamin C. A stool portion in a clean container, without urine. Details: Preparation: stool.
When a retest makes sense
With a positive result the doctor sets the next steps (usually colonoscopy). With a negative one, screening repeats every 1–2 years after 50.
Who usually reviews this result
An out-of-range result is usually reviewed by: Primary care physician, gastroenterologist, proctologist. Bring your report and any previous results to the visit.
Names used on lab reports
Look for one of these names on your report: Fecal occult bloodFITFOBGuaiac testOccult blood
Several markers on your report?
The app reads your whole report — this marker together with its neighbors, not one by one.
A positive fecal occult blood test — is it cancer?
No: more often the cause is benign — hemorrhoids, fissures, polyps, inflammation. But the result cannot be shelved: the doctor decides on colonoscopy — that is how screening catches disease early.
Do I need a diet before the test?
Depends on the method: immunochemical (FIT) needs no diet; the guaiac one needs 3 days without meat, fish, iron and vitamin C. Check the method with your lab.
From what age should I screen?
Colon cancer screening is recommended from 45–50 every 1–2 years; with a family history — earlier, on the doctor’s plan.
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