Occult blood refers to small traces of blood that a person cannot see in their stool. The presence of blood in the stool could be a sign of an underlying condition. Health experts often use this test as a screening tool for the early detection of bowel cancer.
Stool samples can provide valuable information about a person’s gastrointestinal system. The presence of blood in the stool is a sign that indicates bleeding somewhere in the digestive tract. This can happen due to a variety of conditions, ranging from mild irritation to serious conditions such as colorectal cancer, also known as bowel cancer.
This article discusses occult blood stool tests, including their purpose, how people can prepare for it, and how to perform the test.
Fecal occult blood tests (FOBTs) describe a noninvasive lab test that checks stool samples for the presence of blood. Occult blood refers to microscopic blood that the naked eye cannot detect. Different types of fecal occult blood tests are available, which vary in their method of detecting blood.
Guaiac fecal occult blood test (gFOBT)
Fecal immunochemical test (FIT)
Stool DNA test (FIT-DNA test)
Health experts often use fecal occult blood tests to
FOBTs may also help find the cause of anemia. Doctors can also use these tests to identify if a person has inflammatory bowel disease (IBD) rather than irritable bowel syndrome (IBS), a similar condition that does not cause bleeding and anemia.
However, a FOBT alone cannot diagnose any condition. If a person receives an irregular result, a doctor may request other tests to determine the potential cause, such as an imaging test.
Some foods and drugs may affect the results of the test. The doctor will provide specific instructions to ensure the accuracy of the test.
- nonsteroidal anti-inflammatory drugs (NSAIDs)
- selective serotonin reuptake inhibitors (SSRIs)
- iron supplements
It is also advisable for a person to avoid the following foods 3 days before testing to prevent false-positive results:
- red or rare meat
- raw fruits
- raw horseradish
- raw turnips
- red radishes
False negatives can also occur in people taking more than 250 milligrams of vitamin C daily.
A person with certain conditions may consider discussing them with their healthcare professional and rearranging when to collect a sample to prevent false-positive results. This can include:
It is also essential for a person to inform the healthcare professional of any vitamins, supplements, herbs, and prescription and nonprescription drugs that they are taking.
How a person will collect and handle the stool sample depends on the type of test and the manufacturer’s instructions.
To perform a gFOBT, a person should collect and store their stool sample in a dry, clean container. It is important not to let urine or water mix with the stool to avoid contamination. They need to use the applicator that comes with the kit to smear a small amount of the stool on a specified area inside the testing card or place it into a tube that comes with the kit.
The test may also require samples from 2–3 separate bowel movements. A person should then label and seal the samples as directed and transport or mail them to the laboratory for testing.
To perform a FIT, a person must first flush the toilet 2–3 times before collecting the sample. A person will then have their bowel movement as usual and should not flush the toilet.
Using a brush from the kit, a person can scrape the stool’s surface for a few seconds. After gently shaking the brush to remove excess water or clumps of stool, they can then rub the brush on the indicated space.
Some kits may require the person to apply another sample on a separate space in the testing card. Kits come with an extra brush, so they should not reuse a used applicator brush. Other kits may require someone to test more than one stool sample. Once done, they should place the appropriate labels and send the sample to the lab for testing.
A positive fecal occult blood test means that the individual has blood in their stool. This
A negative test result means that the test did not detect blood in the sample. A doctor may then suggest a person repeats the test in a year. An unclear result may suggest that the test was faulty or that it identified a hint of blood but not enough for a positive result. A doctor will likely suggest that a person repeats the test.
A fecal occult blood test is an important tool that checks for small amounts of blood in the stool. This test can give doctors valuable information about the health of the gastrointestinal tract.
Health experts often use a fecal occult blood test to screen for colorectal cancer, but it can also detect other conditions that cause bleeding. If a person receives a positive result, they should consult their doctor for further investigation.