A Hemoccult® test is a medical test used to check for hidden blood in the stool. Bleeding in the gastrointestinal tract can sometimes occur at a very low level, without any visible blood in the stool. Catching bleeds when they are relatively small can be important for providing prompt and appropriate medical treatment to patients with gastrointestinal bleeds. Patients can collect samples at home or have samples collected at a clinic or hospital.
The Hemoccult® is one among a family of tests known as fecal occult blood tests (FOBT). The “occult” in the name refers not to esoteric religious practices, but rather to the hidden nature of blood associated with small bleeds. These tests can be designed in a number of different ways and the Hemoccult® tests rely on a substance called guaiac, which responds to heme in the blood. These tests are not as sensitive as newer tests that search for globin in the stool.
To use a Hemocult® test, patients or clinicians smear a small stool sample onto a paper card and drip hydrogen peroxide on the sample. If heme is present, it will react to quickly oxidize the guaiac and cause a rapid color change. If it is not, a color change will still occur, but much more slowly. This test allows doctors to identify blood loss levels as low as a few teaspoons a day. It is possible to have a false negative if patients are losing less blood than this or if a sample happens to be taken from a relatively clean stool.
This test can also react to certain dietary factors, red meat in particular. Patients may be directed to comply with fasting instructions before a sample is taken, depending on the version of the Hemoccult® test used. It is important to comply with these directions to avoid getting a false positive on the test.
Using Hemoccult® tests is a fast and inexpensive way to screen patients for gastrointestinal bleeds associated with conditions like polyps, cancer, and other bowel diseases. This allows a doctor to determine if additional testing, such as endoscopy to look for bleeding sites, is needed. The test is not recommended for patients with obviously bloody stool, as the presence of blood confirms the presence of a bleed and indicates that it is advisable to move directly to diagnostic tools to find and treat the bleed. If people find blood in their stool, they should contact a doctor immediately.