Fecal Occult Blood Test

The Fecal Occult Blood Test (FOBT) checks for hidden (occult) blood in your stool, which you cannot see. This test is a common screening tool for colorectal cancer and can also help find other causes of bleeding in the digestive tract. Detecting blood early can lead to further investigation and potentially better health outcomes.

What is Fecal Occult Blood Test?

The Fecal Occult Blood Test (FOBT) is a simple test that looks for tiny amounts of blood in your stool (poop) that are not visible to the naked eye. This "occult" or hidden blood can be a sign of various digestive conditions, including polyps or cancer in the colon or rectum, making it a valuable screening tool.

Hidden blood in stool can come from anywhere along your digestive tract, from the esophagus to the rectum. While not always serious, it can sometimes indicate conditions like ulcers, diverticulosis, hemorrhoids, or inflammatory bowel disease. More importantly, it is a key indicator that prompts further investigation for colorectal cancer. There are two main types of FOBT. One is the guaiac-based FOBT (gFOBT), which uses a chemical reaction to detect a substance in blood called heme. The other is the Fecal Immunochemical Test (FIT), which specifically detects human hemoglobin, a protein found in red blood cells. The FIT is generally preferred because it is more specific to human blood and typically does not require changes to your diet or medications before the test. The gFOBT, however, can be affected by certain foods and medicines, requiring specific preparations to ensure accurate results.

Why it's ordered

A Fecal Occult Blood Test is primarily ordered as a screening tool to detect early signs of colorectal cancer, often before symptoms appear. Finding hidden blood can prompt further tests, like a colonoscopy, to identify the source of bleeding. This early detection is crucial for improving treatment outcomes and reducing mortality from colorectal cancer.

Colorectal cancer often begins as small, non-cancerous growths called polyps in the colon or rectum. Over time, some of these polyps can become cancerous. These polyps or early cancers may bleed intermittently, and the FOBT can detect this hidden blood. Regular screening with tests like the FOBT is recommended for people at average risk of colorectal cancer, usually starting around age 45 or 50, depending on guidelines. The goal is to find cancer early when it is most treatable. Studies have shown that screening with FOBT can reduce colorectal cancer mortality by about 15%. Beyond cancer screening, your doctor might order an FOBT if you have symptoms like unexplained abdominal pain, changes in bowel habits, or anemia, to help identify if internal bleeding is contributing to your condition. However, it's most commonly used for routine screening in healthy individuals.

How to prepare

Preparation for a Fecal Occult Blood Test depends on the type of test you are taking. If you are using a Fecal Immunochemical Test (FIT), no special dietary or medication changes are usually needed. For a guaiac-based FOBT (gFOBT), you will need to follow specific instructions regarding diet and certain medications for several days before collecting samples.

For a gFOBT, your doctor will likely advise you to avoid red meat (like beef, lamb, or pork) for at least three days before and during the collection period. Certain fruits and vegetables, such as broccoli, turnips, radishes, and horseradish, may also need to be avoided. These foods can contain substances that interfere with the test, potentially causing a false positive result. You might also be asked to stop taking certain medications and supplements for several days before a gFOBT. This includes aspirin, nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen or naproxen, and vitamin C supplements. Iron supplements can also affect the test results. Always discuss your current medications with your doctor before starting the test. It is important to follow all instructions provided by your doctor or the test kit precisely. If you are unsure about any preparation steps, contact your healthcare provider for clarification. Proper preparation helps ensure the most accurate test results.

What to expect during

During a Fecal Occult Blood Test, you will collect small stool samples at home using a special kit provided by your doctor. You typically collect samples from three separate bowel movements, usually over consecutive days. The process involves using an applicator to smear a small amount of stool onto a test card, which you then return to your doctor or a lab.

Your test kit will contain detailed instructions, test cards, and applicators. You will usually collect a small sample from different parts of a bowel movement. It's important not to mix urine or toilet water with the stool sample, as this can affect the test's accuracy. After collecting the sample, you will apply it to the designated area on the test card. Some kits require you to apply samples from two different spots of the same stool sample to the card. You will then seal the card and repeat this process for the next two bowel movements, often on consecutive days. Once all samples are collected, you will return the completed test cards to your doctor's office or a laboratory as instructed. The samples are then analyzed to check for the presence of hidden blood. The collection process is generally simple and can be done privately in your home.

Understanding your results

Your Fecal Occult Blood Test results will typically be reported as either "positive" or "negative." A positive result means hidden blood was detected in your stool, while a negative result means no blood was found. It is crucial to remember that a positive FOBT does not diagnose cancer; it only indicates the need for further investigation to find the source of the bleeding.

If your FOBT result is negative, it means no hidden blood was found in the samples you provided. This is generally good news, but it does not completely rule out the possibility of polyps or cancer, as these conditions may not bleed all the time. Your doctor will advise you on when you should have your next screening test, usually annually or biennially. A positive FOBT result means blood was detected. This could be due to various reasons, such as hemorrhoids, diverticulosis, ulcers, or inflammatory bowel disease. While it could indicate colorectal cancer or precancerous polyps, it is not a diagnosis. Your doctor will almost certainly recommend a follow-up procedure, most commonly a colonoscopy, to examine your colon and rectum more closely and determine the cause of the bleeding. It is important to discuss your results thoroughly with your healthcare provider. They will interpret the findings in the context of your overall health, medical history, and risk factors. They will guide you on the next steps, whether it's further testing or continuing with routine screening.

Risks

The Fecal Occult Blood Test itself carries no physical risks, as it is a non-invasive test performed at home. However, there are potential implications related to the accuracy of the results. These include the possibility of false positives, which can cause anxiety and lead to unnecessary follow-up procedures, and false negatives, which might delay the diagnosis of a serious condition.

A false positive result occurs when the test indicates the presence of blood, but no actual bleeding from a significant condition is found upon further investigation. This can happen if you didn't follow dietary restrictions for a gFOBT or if the blood is from a minor, non-serious source like hemorrhoids. False positives can lead to anxiety and the need for additional tests, such as a colonoscopy, which carries its own small risks. Conversely, a false negative result means the test does not detect blood, even though a condition like polyps or cancer is present. This can happen if the bleeding is intermittent, or if the specific area of concern did not bleed during the sample collection period. False negatives can provide a false sense of security and potentially delay the diagnosis and treatment of a serious condition. Despite these limitations, the FOBT remains a valuable screening tool. Your clinician will consider your individual risk factors and the specific type of FOBT used when interpreting your results and recommending subsequent actions. It's important to discuss any concerns you have about the test or its results with your doctor.

Frequently asked questions

How often should I get a Fecal Occult Blood Test?

The frequency of FOBT screening depends on your age, risk factors, and the specific type of test. For individuals at average risk of colorectal cancer, annual or biennial screening is often recommended. Your doctor will advise you on the most appropriate screening schedule for your personal health needs.

Can certain foods or medications affect my FOBT results?

Yes, for guaiac-based FOBTs (gFOBT), certain foods like red meat and some vegetables, as well as medications like aspirin, NSAIDs, and vitamin C supplements, can interfere with the test and cause false results. Fecal Immunochemical Tests (FIT) are generally not affected by diet or medication. Always follow your doctor's specific preparation instructions.

What if my FOBT result is positive? Does it mean I have cancer?

A positive FOBT result means hidden blood was found in your stool, but it does not mean you have cancer. Many non-cancerous conditions, such as hemorrhoids or ulcers, can also cause bleeding. A positive result simply indicates that further investigation, usually a colonoscopy, is needed to find the source of the bleeding and determine its cause.

Is the Fecal Occult Blood Test painful?

No, the Fecal Occult Blood Test is not painful. It is a non-invasive test that you perform at home by collecting small stool samples. There are no needles, procedures, or discomfort involved in the test itself.

What is the difference between gFOBT and FIT?

The main difference lies in what they detect and how they are affected by diet. Guaiac-based FOBT (gFOBT) detects a substance in blood called heme and can be affected by certain foods and medications. The Fecal Immunochemical Test (FIT) specifically detects human hemoglobin and typically does not require dietary or medication restrictions, making it generally more specific and easier to prepare for.

If my FOBT is negative, do I still need other colorectal cancer screenings?

A negative FOBT is a good sign, but it doesn't completely rule out all possibilities of polyps or cancer, as bleeding can be intermittent. Your doctor will consider your overall risk factors and may still recommend other screening methods, or advise on the timing of your next FOBT, to ensure comprehensive colorectal cancer screening.

Sources

• MedlinePlus — Fecal Occult Blood Test
• Mayo Clinic — Fecal Occult Blood Test
• Cochrane Library — Fecal Occult Blood Test