Fecal Occult Blood Test - Purpose, Procedure, Results Interpretation, Normal Values and more

The Fecal Occult Blood Test (FOBT) is an essential screening tool that helps detect hidden (occult) blood in a person’s stool. This test is primarily used to identify early signs of gastrointestinal bleeding, which can be a symptom of various medical conditions, including colorectal cancer, ulcers, and polyps. Early detection of these conditions can significantly improve treatment outcomes, making the FOBT a crucial diagnostic tool.

What is a Fecal Occult Blood Test?

The Fecal Occult Blood Test is a non-invasive procedure that tests a sample of stool (feces) for traces of blood that are not visible to the naked eye. Occult blood can be an early sign of several conditions, including gastrointestinal disorders and cancers, such as colorectal cancer, that may not yet show visible symptoms.

The test is called “occult” because the blood present in the stool is not apparent to the individual without laboratory testing. The presence of hidden blood in the stool could be due to conditions like colorectal polyps, ulcers, diverticular disease, or colorectal cancer, all of which can lead to bleeding in the gastrointestinal tract.

How Does the Fecal Occult Blood Test Work?

The Fecal Occult Blood Test works by detecting small amounts of blood in stool that may not be visible to the patient. The test typically uses a chemical reaction to identify hemoglobin, the oxygen-carrying protein found in red blood cells, present in stool samples. The presence of blood in the stool can indicate gastrointestinal bleeding.

There are two main types of FOBT:

• Guaiac-based Fecal Occult Blood Test (gFOBT): This is the traditional method and relies on the chemical guaiac to react with hemoglobin in the blood.
• Immunochemical Fecal Occult Blood Test (iFOBT): This newer method uses antibodies to detect human hemoglobin specifically, which tends to provide more accurate results compared to the guaiac test.

Both types of FOBT are generally simple to administer and can be done at home with a sample of stool, after which the sample is sent to a laboratory for analysis.

Uses of the Fecal Occult Blood Test

• Colorectal Cancer Screening: FOBT is widely used for screening individuals at average risk for colorectal cancer, especially those over 50 years old. Regular screening can help detect early signs of cancer before symptoms appear, significantly improving the chances of successful treatment.
• Detecting Gastrointestinal Disorders: The test helps diagnose gastrointestinal conditions such as ulcers, diverticulosis, and hemorrhoids, which can cause hidden blood loss.
• Monitoring Patients with Known Gastrointestinal Conditions: For individuals already diagnosed with conditions like Crohn’s disease or peptic ulcers, the FOBT can help monitor ongoing bleeding.
• Detecting Polyps: The test can also detect bleeding caused by colorectal polyps, which can potentially develop into cancer if left untreated.

How to Prepare for the Fecal Occult Blood Test

• Dietary Restrictions: For the guaiac-based FOBT (gFOBT), you may be advised to avoid certain foods that could interfere with the results. These foods include red meat, certain fruits and vegetables (such as broccoli and turnips), and certain medications like aspirin or anti-inflammatory drugs, which can irritate the gastrointestinal tract and potentially lead to false positives. Follow your doctor’s specific dietary instructions.
• Medications: Some medications, including blood thinners, may need to be paused before the test. Always consult your healthcare provider before stopping any medications.
• Sample Collection: The test involves collecting a small stool sample, usually over several days. The healthcare provider will give instructions on how to collect and handle the sample properly. Ensure that you follow these instructions closely to avoid contamination of the sample.
• No Special Preparation for iFOBT: If you are undergoing an immunochemical fecal occult blood test (iFOBT), no special dietary or medication restrictions are required. This test is more specific to human hemoglobin and tends to be less affected by food and drug intake.

How to Perform the Fecal Occult Blood Test

1. Sample Collection: The most common method for collecting the stool sample is using a collection kit that your doctor provides. The kit will contain everything you need to take a sample of your stool and return it to the lab for analysis. Typically, you’ll need to collect small amounts of stool on separate occasions over several days.
2. Guaiac-Based Test: In the guaiac test, the stool sample is placed on a special card, and a developer chemical is applied to detect the presence of blood. A blue color change indicates a positive result, meaning blood was detected.
3. Immunochemical Test: For the immunochemical test, the stool sample is mixed with a reagent that binds specifically to human hemoglobin. If blood is present, a color change occurs, indicating a positive result.

Interpretation of Fecal Occult Blood Test Results

Once the stool sample is analyzed in the laboratory, your healthcare provider will receive the results. The results can be categorized as follows:

• Negative Result: If no blood is detected in the stool, the test result is negative, suggesting no gastrointestinal bleeding at the time of testing.
• Positive Result: If blood is detected, the result is positive. However, a positive result does not necessarily indicate cancer or a serious condition. There are many benign reasons for blood to appear in the stool, such as hemorrhoids, anal fissures, or gastric ulcers. Further testing, such as colonoscopy, may be recommended to determine the cause of the bleeding.
• False Positives and False Negatives: The FOBT is a sensitive test, but it’s not perfect. Certain foods, medications, or conditions may cause false-positive results, while bleeding that is intermittent or very small may result in a false-negative test. This is why the test is often used as part of a larger diagnostic workup.

Normal Range for Fecal Occult Blood Test

There is no “normal” or “abnormal” range for the Fecal Occult Blood Test itself because the goal is to determine the presence or absence of blood. A negative result means that no blood was detected, which is generally considered normal. A positive result indicates the presence of blood, which requires further investigation.

If your test results are positive, your doctor will discuss next steps, which may include additional testing such as colonoscopy or imaging studies, depending on your symptoms and risk factors.

Risks and Complications of the Fecal Occult Blood Test

• False Positives: Certain foods or medications can lead to false positives, which can result in unnecessary follow-up tests or procedures.
• False Negatives: The test may miss blood in the stool, especially if the bleeding is intermittent. This can lead to a false sense of security and delay diagnosis.
• Emotional Stress: A positive result can cause anxiety, even if the cause of the bleeding is not cancerous. It is important to work closely with your healthcare provider to understand the results and next steps.

Benefits of the Fecal Occult Blood Test

• Early Detection: The FOBT can detect gastrointestinal bleeding before visible symptoms appear, which is crucial for early diagnosis and treatment of conditions like colorectal cancer.
• Non-Invasive: The test is simple and non-invasive, allowing individuals to collect samples at home with minimal discomfort.
• Cost-Effective: The FOBT is a relatively inexpensive test that provides valuable information about gastrointestinal health, making it accessible for routine screening.
• Potential for Life-Saving Early Diagnosis: By detecting early signs of cancer, ulcers, or other conditions, the FOBT can help prevent serious health issues by prompting early intervention and treatment.

FAQs About the Fecal Occult Blood Test

1. What is a Fecal Occult Blood Test?

A Fecal Occult Blood Test (FOBT) is a screening tool used to detect hidden blood in the stool, which can be a sign of gastrointestinal bleeding caused by conditions like colorectal cancer, ulcers, or polyps. It is non-invasive and typically performed at home.

2. How do I collect a sample for the FOBT?

You will receive a collection kit from your doctor, which typically includes a card or container to collect small amounts of stool. You may need to collect samples over several days, following the instructions provided by your healthcare provider.

3. What does a positive FOBT result mean?

A positive FOBT result means blood was detected in your stool. This could be due to various conditions, including hemorrhoids, ulcers, or colorectal cancer. Further testing is often necessary to determine the cause of the bleeding.

4. How accurate is the FOBT?

While the FOBT is a useful tool, it is not 100% accurate. False positives can occur due to dietary or medication factors, and false negatives can happen if the bleeding is not consistent. Your doctor will help interpret the results and recommend additional testing if needed.

5. Do I need to stop taking any medications before the test?

Certain medications, such as blood thinners or aspirin, may need to be temporarily discontinued before the test, as they can affect the results. Always consult with your doctor before stopping any medications.

6. What foods should I avoid before taking the test?

For the guaiac-based FOBT, you may be advised to avoid red meat, certain vegetables, and certain medications for a few days before the test, as they can interfere with the results. Follow your healthcare provider’s dietary instructions carefully.

7. How often should I take the Fecal Occult Blood Test?

The FOBT is commonly recommended for individuals over 50 years old as part of routine colorectal cancer screening. Your doctor will determine how often you need the test based on your risk factors, family history, and overall health.

8. What should I do if my FOBT result is positive?

If your result is positive, your doctor will likely recommend further testing, such as a colonoscopy, to identify the source of the bleeding and determine the appropriate treatment.

9. Can I take the test at home?

Yes, the FOBT can often be performed at home using a collection kit provided by your healthcare provider. You will collect the stool sample, follow the instructions, and send it to a laboratory for analysis.

10. Are there any risks associated with the FOBT?

The FOBT is a safe and non-invasive test with minimal risks. However, the potential for false-positive or false-negative results can lead to unnecessary tests or missed diagnoses. It is important to work closely with your healthcare provider to understand your results.

Conclusion

The Fecal Occult Blood Test is an invaluable tool for early detection of gastrointestinal issues, including colorectal cancer and other conditions that cause gastrointestinal bleeding. While the test is not perfect, it provides an essential screening mechanism that can help save lives by identifying problems early. By understanding how the test works, how to prepare for it, and what the results mean, you can make informed decisions about your health and well-being. Always follow up with your healthcare provider for further tests if necessary to ensure that you receive the best care possible.