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What is Fecal Occult Blood Test? Purpose, Levels/Procedure & Result

Created at:1/13/2025

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A fecal occult blood test checks for hidden blood in your stool that you can't see with your eyes. This simple screening test helps doctors detect bleeding anywhere in your digestive system, from your stomach down to your rectum. The word "occult" simply means hidden or invisible, so this test finds blood that's there but not obvious to you.

What is fecal occult blood test?

The fecal occult blood test is a screening tool that detects microscopic amounts of blood in your stool sample. Your digestive tract can bleed for many reasons, and sometimes this bleeding is so small that you won't notice any changes in your bowel movements.

There are two main types of this test. The guaiac-based test (gFOBT) uses a chemical reaction to find blood, while the immunochemical test (FIT) uses antibodies to detect human blood proteins. Both tests serve the same purpose but work slightly differently.

This test is particularly valuable because it can catch problems early, often before you develop any symptoms. Many conditions that cause intestinal bleeding start small and gradually worsen over time.

Why is fecal occult blood test done?

Doctors recommend this test primarily to screen for colorectal cancer and pre-cancerous polyps. Early detection of these conditions dramatically improves treatment outcomes and survival rates.

The test also helps investigate unexplained symptoms like fatigue, weakness, or iron deficiency anemia. Sometimes your body shows signs of blood loss before you notice any digestive symptoms.

Beyond cancer screening, this test can detect other conditions that cause intestinal bleeding. These include inflammatory bowel disease, ulcers, diverticulosis, and various infections that affect your digestive system.

Most healthcare providers recommend regular screening starting at age 45 to 50 for people at average risk. If you have family history of colorectal cancer or other risk factors, your doctor might suggest starting earlier.

What is the procedure for fecal occult blood test?

The procedure is straightforward and you can do it at home with a kit from your doctor's office. You'll collect small samples of your stool over several days, usually from three different bowel movements.

Here's what the process typically involves:

  1. Your doctor gives you a test kit with detailed instructions
  2. You collect small stool samples using the provided tools
  3. You place samples on special test cards or in collection tubes
  4. You return the samples to your doctor's office or lab
  5. Lab technicians analyze your samples for blood

The immunochemical test (FIT) usually requires only one sample, while the guaiac test typically needs samples from three different bowel movements. This helps increase the accuracy of detecting any bleeding.

Results are usually available within a few days to a week. The lab will send results to your doctor, who will then contact you to discuss what they found.

How to prepare for your fecal occult blood test?

Preparation depends on which type of test you're taking. The FIT test requires minimal preparation since it specifically detects human blood and isn't affected by foods.

For the guaiac test, you'll need to avoid certain foods and medications for a few days before testing. This is because some substances can cause false positive or false negative results.

Foods to avoid before a guaiac test include:

  • Red meat (beef, lamb, pork)
  • Raw vegetables high in peroxidase (turnips, radishes, broccoli)
  • Citrus fruits and juices
  • Iron supplements

You should also avoid certain medications like aspirin, ibuprofen, and other blood thinners if your doctor approves. These can increase bleeding risk and affect test results.

Don't collect samples during your menstrual period, as this can contaminate the test. Wait at least three days after your period ends before collecting samples.

How to read your fecal occult blood test?

Test results are reported as either positive or negative. A negative result means no blood was detected in your stool samples, which is the normal and expected finding.

A positive result indicates that blood was found in your stool. However, this doesn't automatically mean you have cancer or a serious condition. Many benign conditions can cause small amounts of bleeding.

It's important to understand that this test is a screening tool, not a diagnostic test. A positive result means you need further testing to determine the source of bleeding. Your doctor will likely recommend a colonoscopy to examine your colon directly.

False positives can occur, especially with the guaiac test, due to certain foods or medications. False negatives are also possible if the bleeding is intermittent or very minimal.

How to fix your fecal occult blood test levels?

You can't directly "fix" a positive fecal occult blood test because it's detecting an underlying condition that needs medical attention. The positive result is actually doing its job by alerting you to investigate further.

If your test is positive, your doctor will recommend additional testing to find the source of bleeding. This usually starts with a colonoscopy, which allows direct visualization of your colon and rectum.

Treatment depends entirely on what's causing the bleeding. Small polyps might be removed during colonoscopy, while infections might need antibiotics. More serious conditions like cancer require specialized oncology care.

The key is not to delay follow-up testing. Early detection and treatment of whatever is causing the bleeding typically leads to much better outcomes.

What is the best fecal occult blood test level?

The best result for a fecal occult blood test is negative, meaning no blood was detected in your stool samples. This suggests that there's no significant bleeding in your digestive tract at the time of testing.

There aren't "levels" of fecal occult blood like there are with other blood tests. The test is qualitative, meaning it either detects blood or it doesn't. It's not measuring how much blood is present.

A consistently negative test over time is reassuring, especially when done as part of regular screening. However, remember that this test only detects bleeding that's happening when you collect the samples.

Some conditions cause intermittent bleeding, which is why doctors often recommend repeating the test annually if you're using it for cancer screening.

What are the risk factors for positive fecal occult blood test?

Several factors can increase your likelihood of having a positive test result. Age is a significant risk factor, as digestive system problems become more common as you get older.

Family history plays an important role, especially for colorectal cancer and inflammatory bowel diseases. If close relatives have had these conditions, your risk increases considerably.

Common risk factors include:

  • Age over 50 years
  • Family history of colorectal cancer or polyps
  • Personal history of inflammatory bowel disease
  • Smoking and heavy alcohol use
  • Diet high in processed meats and low in fiber
  • Sedentary lifestyle and obesity

Certain medications can also increase bleeding risk. These include blood thinners, aspirin, and nonsteroidal anti-inflammatory drugs when used regularly.

Having risk factors doesn't guarantee a positive test, but it does mean you should be more vigilant about screening and follow-up care.

Is it better to have high or low fecal occult blood test result?

A negative (low) fecal occult blood test result is always better than a positive (high) result. This test doesn't measure levels in the traditional sense, but rather detects the presence or absence of blood.

A negative result suggests that your digestive tract isn't bleeding significantly at the time of testing. This is reassuring and indicates that serious conditions like colorectal cancer are less likely.

However, a positive result isn't necessarily catastrophic news. Many conditions that cause positive results are treatable, especially when caught early. The test is actually protecting you by alerting you to investigate further.

The most important thing is to follow through with recommended testing if your result is positive. Early detection and treatment of whatever is causing the bleeding typically leads to much better outcomes.

What are the possible complications of negative fecal occult blood test?

A negative test result is generally good news, but it's not 100% guarantee that you don't have any digestive system problems. The main limitation is that this test only detects bleeding that's happening when you collect samples.

Some cancers and polyps don't bleed continuously, so they might be missed if they're not bleeding during your test period. This is why doctors recommend regular screening rather than one-time testing.

Very small amounts of bleeding might fall below the test's detection threshold. Additionally, bleeding from the upper digestive tract (stomach, small intestine) might be broken down by digestive enzymes and not detected.

False negative results can occur if you're taking certain medications or if there are technical issues with sample collection or processing. This is why proper preparation and following instructions carefully is so important.

What are the possible complications of positive fecal occult blood test?

A positive test result mainly creates anxiety and the need for further testing, rather than direct physical complications. The emotional stress of waiting for follow-up results can be significant for many people.

The more serious concern is delaying the recommended follow-up testing. Whatever is causing the bleeding could potentially worsen if left untreated, especially if it's a pre-cancerous condition.

False positive results can lead to unnecessary anxiety and additional testing. This is more common with the guaiac test, especially if dietary restrictions weren't followed properly.

Financial implications can include the cost of follow-up procedures like colonoscopy. However, most insurance plans cover these procedures when they're medically necessary based on positive screening results.

The key is to remember that a positive result is an opportunity for early detection and treatment, not a diagnosis of something serious.

When should I see a doctor for fecal occult blood test?

You should see a doctor if you have a positive fecal occult blood test result. Don't wait or hope it will go away on its own – prompt follow-up is crucial for your health.

Contact your doctor immediately if you notice visible blood in your stool, even if you haven't had this test. Black, tarry stools or bright red blood are signs that need immediate medical attention.

Other symptoms that warrant medical evaluation include:

  • Persistent changes in bowel habits
  • Unexplained weight loss
  • Persistent abdominal pain or cramping
  • Unusual fatigue or weakness
  • Iron deficiency anemia

Even with a negative test, you should see your doctor if you develop concerning symptoms. The test only shows what's happening at the time of collection, not your overall digestive health.

Regular screening discussions with your doctor are important, especially as you age or if you have family history of colorectal problems.

Frequently asked questions about Fecal occult blood test

Yes, the fecal occult blood test is an effective screening tool for colorectal cancer, especially when used regularly. Studies show that annual screening with this test can reduce colorectal cancer deaths by 15-33%.

However, it's not perfect. The test can miss cancers that aren't bleeding at the time of testing, and it can't detect all polyps. That's why some doctors recommend combining it with other screening methods or using colonoscopy instead.

No, a positive test doesn't mean you have cancer. Many benign conditions can cause bleeding, including hemorrhoids, anal fissures, ulcers, and infections. In fact, most positive results are due to non-cancerous causes.

The test is designed to be sensitive, meaning it catches most cases of bleeding but also picks up many harmless causes. This is why follow-up testing with colonoscopy is so important to determine the actual cause.

Most medical guidelines recommend annual fecal occult blood testing for colorectal cancer screening in average-risk adults starting at age 45-50. Your doctor might recommend more frequent testing if you have risk factors.

If you're using this test for screening, consistency is key. Annual testing is more effective than sporadic testing because it increases the chance of detecting intermittent bleeding.

Yes, certain medications can affect test results. Blood thinners like warfarin or aspirin can increase bleeding risk and potentially cause positive results. Some medications can also interfere with the chemical reactions used in testing.

Always tell your doctor about all medications you're taking, including over-the-counter drugs and supplements. They can advise whether you need to stop anything before testing.

If you're having trouble collecting samples due to constipation or other issues, contact your doctor's office. They can provide advice on safe ways to encourage bowel movements or discuss alternative testing methods.

Don't use laxatives without checking with your doctor first, as some can affect test results. Simple dietary changes like increasing fiber and water intake might help naturally.

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