The presence of blood in stool can be a concerning symptom for many individuals, often prompting a visit to the doctor to determine the underlying cause. One of the most common diagnostic tools used to detect blood in stool is the fecal blood test, also known as the fecal occult blood test (FOBT) or guaiac fecal occult blood test (gFOBT). This non-invasive test has been widely used for decades to screen for colorectal cancer, as well as other gastrointestinal disorders that may cause bleeding in the digestive tract.
What is a Fecal Blood Test?
A fecal blood test is a laboratory examination designed to detect the presence of blood in stool samples. The test is based on the principle that blood contains the protein hemoglobin, which can be detected using chemical reagents. During the test, a small sample of stool is collected and applied to a special card or device containing the reagent. If blood is present in the stool, the reagent will react with the hemoglobin, producing a color change that indicates a positive result.
Types of Fecal Blood Tests
There are several types of fecal blood tests available, each with its own advantages and limitations. The most common types include:
- Guaiac Fecal Occult Blood Test (gFOBT): This is the traditional type of fecal blood test, which uses a guaiac-based reagent to detect blood in stool. The test is relatively inexpensive and easy to perform but may produce false-positive results due to dietary factors, such as consuming red meat or certain vegetables.
- Immunochemical Fecal Occult Blood Test (iFOBT): This type of test uses antibodies to detect human hemoglobin in stool samples. iFOBT is more specific than gFOBT and less prone to false-positive results.
- Fecal Immunochemical Test (FIT): This is a more advanced type of iFOBT that uses a specific antibody to detect human hemoglobin. FIT is highly sensitive and specific, making it an ideal choice for colorectal cancer screening.
How is a Fecal Blood Test Performed?
The procedure for performing a fecal blood test is relatively simple and non-invasive. Here’s a step-by-step overview:
- Stool Sample Collection: A small sample of stool is collected from the patient using a special collection device or a cardboard container.
- Sample Preparation: The stool sample is then applied to a special card or device containing the reagent.
- Incubation: The sample is allowed to incubate for a specified period, usually 5-10 minutes.
- Result Interpretation: The test result is then interpreted based on the color change or absence of color change.
What Do Fecal Blood Test Results Mean?
A positive result on a fecal blood test indicates the presence of blood in the stool, which may be a sign of an underlying gastrointestinal disorder, such as:
- Colorectal cancer
- Diverticulitis
- Ulcerative colitis
- Crohn’s disease
- Gastrointestinal bleeding
A negative result, on the other hand, suggests that no blood is present in the stool. However, it’s essential to note that a negative result does not entirely rule out the presence of a gastrointestinal disorder, as some conditions may not cause bleeding.
Limitations and Potential False-Positive Results
While fecal blood tests are widely used and generally reliable, there are some limitations and potential false-positive results to be aware of:
- Dietary Interference: Certain foods, such as red meat, turnips, and horseradish, can cause false-positive results on gFOBT.
- Medications: Aspirin, ibuprofen, and other non-steroidal anti-inflammatory drugs (NSAIDs) can increase the risk of gastrointestinal bleeding, leading to false-positive results.
- Infection: Gastrointestinal infections, such as gastritis or diverticulitis, can cause inflammation and bleeding, leading to false-positive results.
Fecal Blood Test vs. Other Diagnostic Tools
Fecal blood tests are often compared to other diagnostic tools, such as:
- Colonoscopy: A colonoscopy is a more invasive procedure that involves inserting a flexible tube with a camera and light on the end to visually examine the colon and rectum.
- Stool DNA Testing: This is a relatively new type of test that detects genetic mutations in stool DNA, which can indicate the presence of colorectal cancer.
While fecal blood tests are non-invasive and relatively inexpensive, they may not be as sensitive or specific as other diagnostic tools. A combination of tests, including fecal blood tests, colonoscopy, and stool DNA testing, may be used to diagnose and monitor gastrointestinal disorders.
Fecal blood tests are a useful diagnostic tool for detecting blood in stool, but it's essential to understand their limitations and potential false-positive results. A combination of tests and a thorough medical evaluation are often necessary to determine the underlying cause of gastrointestinal symptoms.
Step-by-Step Guide to Preparing for a Fecal Blood Test
- Stop taking aspirin, ibuprofen, and other NSAIDs for 7-10 days before the test.
- Avoid eating red meat, turnips, and horseradish for 3-5 days before the test.
- Collect a small sample of stool using a special collection device or a cardboard container.
- Apply the stool sample to the test card or device according to the manufacturer's instructions.
- Allow the sample to incubate for the recommended period.
- Interpret the test result based on the color change or absence of color change.
What is the purpose of a fecal blood test?
+The purpose of a fecal blood test is to detect the presence of blood in stool, which can be a sign of an underlying gastrointestinal disorder, such as colorectal cancer, diverticulitis, or ulcerative colitis.
How accurate is a fecal blood test?
+The accuracy of a fecal blood test depends on the type of test and the laboratory procedures used. Generally, iFOBT and FIT are more sensitive and specific than gFOBT.
Can a fecal blood test detect other conditions besides colorectal cancer?
+Yes, a fecal blood test can detect other conditions that cause gastrointestinal bleeding, such as diverticulitis, ulcerative colitis, and Crohn’s disease.
