From the Guidelines
FOBT and stool guaiac test are not exactly the same, but guaiac-based FOBT is a specific type of fecal occult blood test that uses guaiac to detect hidden blood in stool samples. The guaiac-based FOBT is a specific type of fecal occult blood test that uses guaiac, a plant resin, to detect hidden (occult) blood in stool samples, as mentioned in 1. This test works by detecting the peroxidase activity of hemoglobin in blood, which causes a color change when it reacts with guaiac in the presence of hydrogen peroxide.
According to the most recent and highest quality study 1, stool-based tests include the high-sensitivity guaiac fecal occult blood test (gFOBT), fecal immunochemical test (FIT), and stool DNA test. Both high-sensitivity gFOBT and FIT detect blood in the stool; however, they use different methods. High-sensitivity gFOBT is based on chemical detection of blood, while FIT uses antibodies to detect blood.
Some key points to consider when using FOBT or stool guaiac test for colorectal cancer screening include:
- Certain foods (red meat, some fruits and vegetables) and medications (NSAIDs like aspirin) can affect test results, so dietary and medication restrictions may be recommended for 2-3 days before the test to avoid false positives, as mentioned in 1.
- The test is commonly used for colorectal cancer screening, as blood in stool can be an early sign of colorectal polyps or cancer.
- Patients typically collect small stool samples at home using a test kit, which are then analyzed in a laboratory or by a healthcare provider.
- Screening with annual FIT or annual sDNA-FIT provides an estimated greater life-years gained than annual high-sensitivity gFOBT or sDNA-FIT every 3 years, as mentioned in 1.
It's worth noting that there is uncertainty around the accuracy of high-sensitivity gFOBT to detect colorectal cancer and advanced adenomas, although it is likely lower than the accuracy of FIT and sDNA-FIT, and high-sensitivity gFOBT is more difficult for patients to administer, as mentioned in 1. However, randomized trials demonstrate direct evidence of decreased deaths from colorectal cancer when screening with non–high-sensitivity gFOBT is performed, as mentioned in 1.
From the Research
FOBT and Stool Guaiac Comparison
- FOBT (Fecal Occult Blood Test) and stool guaiac are related but not exactly the same thing. Stool guaiac refers to a specific type of FOBT that uses guaiac as a reagent to detect blood in stool 2, 3, 4, 5, 6.
- Guaiac-based FOBT (G-FOBT) is an older method that has been widely used for colorectal cancer screening, but it has limitations in terms of sensitivity and specificity 2, 3, 5, 6.
- Immunochemical FOBT (I-FOBT) is a newer method that uses antibodies to detect human hemoglobin in stool, and it has been shown to have improved sensitivity and specificity compared to G-FOBT 3, 4, 5, 6.
- Studies have compared the performance of G-FOBT and I-FOBT in screening for colorectal cancer, and the results suggest that I-FOBT has a higher sensitivity and detection rate for advanced adenomas and cancer 5, 6.
Key Differences
- Sensitivity: I-FOBT has been shown to have a higher sensitivity than G-FOBT for detecting colorectal cancer and advanced adenomas 3, 5, 6.
- Specificity: G-FOBT has been shown to have a higher specificity than I-FOBT, but the difference is not always significant 3, 5, 6.
- Positivity rate: I-FOBT has been shown to have a higher positivity rate than G-FOBT, which can lead to more false positives but also more true positives 5, 6.
Clinical Implications
- The choice of FOBT method depends on the clinical setting and the desired balance between sensitivity and specificity 4, 5, 6.
- I-FOBT may be preferred for screening populations due to its higher sensitivity and detection rate for advanced adenomas and cancer 5, 6.
- G-FOBT may still be useful in certain clinical settings, such as in patients with a low risk of colorectal cancer or in resource-limited areas 2, 3.