Fecal Occult Blood (Occult Blood in Stool)

What is a fecal occult blood test?

A fecal occult blood test is done to detect blood in the stool in amounts too small to be noticed with the naked eye. Small bleeds in the digestive tract that cause no symptoms may not change the color of the stool. Such bleeding can be the first sign of various conditions, such as polyps, inflammation, hemorrhoids or colorectal cancer. Because treatment success increases markedly when colorectal cancer is caught at an early stage, this simple test plays an important role in screening programs.

The immunochemical method widely used today recognizes blood by means of antibodies specific to human hemoglobin and is particularly sensitive to bleeding from the large intestine. Older guaiac-based methods, by contrast, measure the chemical activity of hemoglobin and can be affected by certain foods. The test result is reported as positive or negative. The test does not show the source of the bleeding; it only helps decide whether further investigation is needed.

When is a fecal occult blood test ordered?

This test is used mostly in screening for the early detection of colorectal cancer in people without symptoms. In Türkiye's national screening program, it is generally recommended every two years for women and men aged 50–70; for people with risk factors such as a family history, the doctor may set a different plan. It may also be ordered in the evaluation of certain digestive complaints.

• Colorectal cancer screening in people at average risk
• Iron-deficiency anemia whose cause is being investigated
• A change in bowel habits that has lasted for weeks
• Unexplained abdominal pain or unintentional weight loss

How do you prepare for a fecal occult blood test?

You do not need to fast before this test. With the immunochemical method there is usually no dietary restriction; if a guaiac-based method is used, red meat, some raw vegetables and high-dose vitamin C may be restricted for a few days. To prevent false-positive results, it is recommended not to give a sample during menstruation, while hemorrhoids are bleeding or when there is blood in the urine. If you take aspirin or a blood thinner, do not stop your medicine on your own; discuss it with your doctor.

The sample is taken with the stick or spoon in the container lid from stool passed onto a clean surface, without mixing with urine or toilet water. If the laboratory requests samples from more than one day, you need to put each sample in a separate container and label the containers. If you want to have the test done at home, the sample container is delivered to you, you collect the sample yourself, and our nurse picks up the container and delivers it to the laboratory. Until you hand it over, store the sample in a cool place out of direct sunlight.

What does a fecal occult blood result mean?

A negative result means that no occult blood was detected in the sample examined. However, because polyps and tumors do not always bleed continuously, a negative result does not completely eliminate the possibility of disease; screening should be repeated at the recommended intervals. If you notice symptoms such as visible blood in the stool or black, tarry stools, you should see a doctor without waiting for the test result.

A positive result suggests bleeding in the digestive tract, but it does not mean cancer. Hemorrhoids, anal fissures, polyps, inflammatory bowel diseases and, depending on the method used, stomach or duodenal ulcers can also cause a positive result. To find the cause of the bleeding, your doctor will usually request further investigations such as a colonoscopy. The method used and the reference wording may vary by laboratory; this laboratory's reference is shown on the page. The result should be interpreted by a doctor together with your symptoms and other findings.