Fecal Occult Blood (FOBT)
Definition
Detects blood that is not visible to the eye (occult) in the stool. It can indicate bleeding anywhere in the digestive tract: polyps, hemorrhoids, ulcers or colorectal cancer.
There are two methods:
| Method | How it works | Number of samples |
|---|---|---|
| gFOBT (guaiac) | Uses a chemical to detect blood | Usually from 2–3 separate bowel movements |
| FIT (immunochemical) | Uses antibodies that bind to hemoglobin; more effective at finding blood | 1–3 samples depending on the brand |
Purpose
A screening test that helps find colorectal cancer before symptoms appear. For people at average risk, starting at age 45 is recommended; earlier for those at high risk.
Results
A positive result indicates that there is bleeding somewhere in your digestive tract; it does not automatically mean cancer.
Risks and Limitations
Diet and medications can cause false positives. Things you may need to avoid before the test: red meat, high-dose vitamin C, NSAID pain relievers and certain vegetables.
A positive result usually requires a colonoscopy for a definitive diagnosis.