From the Guidelines
A Fecal Immunochemical Test (FIT) cannot reliably distinguish hemorrhoid bleeding from other sources of gastrointestinal bleeding. FIT tests detect human globin, a protein that constitutes human hemoglobin, in stool samples, but they cannot identify the specific source of the blood 1. While hemorrhoids are a common cause of rectal bleeding, a positive FIT result could indicate bleeding from hemorrhoids, colorectal polyps, colorectal cancer, inflammatory bowel disease, or other conditions in the digestive tract.
Key Points to Consider
- The test only detects the presence of blood, not its origin, which is a significant limitation in diagnosing the cause of bleeding.
- FIT has several technological advantages over guaiac-based tests, including higher specificity for human blood and lower gastrointestinal bleeding 1.
- However, these advantages do not extend to distinguishing between different sources of lower gastrointestinal bleeding.
Implications for Clinical Practice
- If a FIT test is positive, further diagnostic procedures such as colonoscopy are typically recommended to determine the exact cause of bleeding.
- Relying solely on the assumption that a positive FIT is due to hemorrhoids could potentially delay diagnosis of more serious conditions like colorectal cancer.
- Anyone with a positive FIT result should follow up with their healthcare provider for appropriate additional testing, even if they have known hemorrhoids.
From the Research
FIT Test and Hemorrhoid Bleeding
- The ability of a Fecal Immunochemical Test (FIT) to distinguish hemorrhoid bleeding is a topic of interest in colorectal cancer screening 2, 3.
- A study published in 2017 found that hemorrhoids are significantly associated with false-positive FIT results, with the presence of hemorrhoids being an independent predictor of false-positive results (adjusted odds ratio, 2.76; 95% confidence interval, 2.24-3.40; p<0.001) 2.
- However, another study from 2012 reported that hemorrhoids detected at colonoscopy are an infrequent cause of false-positive FIT results, with only 4.1% of individuals with false-positive results having hemorrhoids as the only abnormality 3.
Factors Influencing FIT Results
- Logistic regression analysis has identified hemorrhoids, nonadvanced polyps, and miscellaneous abnormalities as factors influencing false-positive FIT results 3.
- The presence of hemorrhoids has been shown to increase the rate of false-positive FIT results, with 24.7% of participants with hemorrhoids having false-positive results compared to 10.5% of those without hemorrhoids (p<0.001) 2.
Limitations and Future Directions
- The current evidence suggests that FIT tests may not be able to reliably distinguish between hemorrhoid bleeding and other sources of bleeding 2, 3.
- Further studies are needed to fully understand the relationship between FIT results and hemorrhoid bleeding, as well as to develop more accurate and reliable screening tests for colorectal cancer 4, 5.