The Stool Occult Blood Test (FOBT), also called a fecal occult blood test or fecal blood test, is a simple lab test that checks a stool sample for hidden (occult) blood. “Occult” means the blood is not visible to the naked eye—you may not notice any red blood in the toilet or on toilet paper. The test looks for tiny amounts of blood that can come from anywhere in the gastrointestinal (GI) tract, including the stomach, small intestine, colon, or rectum.

FOBT is commonly used as a screening test for colon cancer (colorectal cancer) and for signs of gastrointestinal bleeding. Small growths in the colon called polyps can sometimes bleed, and some polyps can develop into cancer over time. Detecting occult blood can be an early clue that further evaluation is needed.

What results may mean:

• Negative/normal: No blood was detected in the sample(s). This is reassuring, but it does not completely rule out polyps, colon cancer, or other GI problems—some conditions bleed intermittently, and bleeding may not be present in every bowel movement.

• Positive/abnormal: Blood was detected. This does not automatically mean cancer. A positive FOBT simply means there may be bleeding somewhere in the digestive tract, and your clinician will usually recommend follow-up testing (often a colonoscopy) to find the source. Other causes include hemorrhoids, inflammation, ulcers, or certain medications.

A stool occult blood test may be ordered for screening or to help evaluate symptoms that suggest possible GI bleeding. It’s a common, noninvasive way to support early detection of colorectal cancer and other digestive health concerns.

Your clinician may recommend FOBT for screening when:

• You are due for colorectal cancer screening based on age and risk level (FOBT is one of several accepted screening options).

• You have an increased risk of colon cancer, such as a strong family history of colorectal cancer or colon polyps, or a personal history of polyps.

It may be ordered to evaluate symptoms or concerns such as:

• Rectal bleeding or blood in/around the stool (even if it seems mild or occasional).

• Unexplained anemia (especially iron-deficiency anemia), fatigue, weakness, or shortness of breath that could be related to slow blood loss.

• Ongoing digestive symptoms such as persistent abdominal pain, unexplained weight loss, or a change in bowel habits (new constipation, diarrhea, or narrower stools).

• Concern for gastrointestinal bleeding from conditions like ulcers, inflammation, or medication-related irritation.

Important note: Different stool blood tests exist. Classic “FOBT” often refers to guaiac-based testing (gFOBT), which can be affected by certain foods and medications. Many screening programs use a newer version called FIT (fecal immunochemical test), which is more specific to human blood from the lower GI tract. Follow the collection instructions from your lab carefully, because preparation and the number of samples collected can vary.

• Colorectal (colon) cancer
• Colon polyps (including adenomas) and polyp screening follow-up
• Gastrointestinal bleeding (occult bleeding)
• Hemorrhoids and anal fissures (common non-cancer causes of bleeding)
• Peptic ulcer disease (stomach or duodenal ulcers)
• Gastritis or esophagitis
• Inflammatory bowel disease (ulcerative colitis, Crohn’s disease)
• Diverticulosis/diverticular bleeding
• Angiodysplasia (fragile blood vessels in the GI tract)
• Colitis due to infection or inflammation

• Colon cancer screening and early detection of colorectal cancer
• Supporting overall digestive health by identifying possible hidden GI bleeding
• Polyp screening strategies and deciding when colonoscopy or further evaluation is needed
• Investigating unexplained iron-deficiency anemia or chronic fatigue potentially linked to slow blood loss
• Monitoring for recurrence of bleeding in people with prior GI bleeding history (as directed by a clinician)
• Risk-based preventive care planning for individuals with family history of colon cancer or polyps