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CancerQuest > Introduction to Patient Information > Introduction to Cancer Detection and Diagnosis > Fecal Occult Blood Tests (FOBT)

Fecal Occult Blood Tests (FOBT)

Fecal occult blood tests (FOBT) are able to detect small hidden (occult) blood present in stools, a possible sign of colon cancer or colonic polyps (precursors of cancer). Occult blood refers to very small amounts of blood that cannot be seen by visual inspection, but can be detected using chemical tests. The detection of blood in stool does not necessarily indicate cancer, it simply helps health care professionals make an accurate diagnosis. There are currently two methods used to detect occult blood, they are described below.

Guaiac Fecal Occult Blood Test (GFOBT)

The GFOBT detects the activity of peroxidase, an enzyme found in the blood. The test can be done using a home kit obtained from a health care provider. It requires a sample taken of the inside and the outside of three separate bowel movements. The samples are then placed on appropriate slides and returned for testing. Some foods, medications, and supplements can cause false positives, so be sure to carefully follow instructions from your health care provider or the test manufacturer.^{(1) (2)}

Fecal Immunochemical Test (FIT)

The fecal immunochemical test is a more advanced, easier to use FOBT that has shown a better combination of sensitivity and specificity. The test uses antibodies to detect the presence of blood hemoglobin. This method is not affected by food, medication, or supplements and it is also easier for subjects to obtain an adequate sample. The FIT only requires samples from the surface of two bowel movements. Although the FIT is more user friendly, it is still important to carefully follow your health care providers instructions.^{(1) (2)}

Learn more about sensitivity and specificity of medical tests

References for this page:

1. Guittet L et al. Comparison of a guaiac based and an immunochemical faecal occult blood test in screening for colorectal cancer in a general average risk population. Gut 2007 Feb; 56:210-4. [PUBMED]
2. A Smith, GP Young, SR Cole, P Bampton. Comparison of a Brush-Sampling Fecal Immunochemical Test for Hemoglobin With a Sensitive Guaiac-Based Fecal Occult Blood Test in Detection of Colorectal Neoplasia. Cancer. 2006;107:21529. [PUBMED]