The Fecal Immunochemical Test (FIT) is a standard non-invasive screening method used to detect hidden blood in the stool, a potential early sign of colorectal cancer or precancerous polyps. Many people worry that common, benign conditions like hemorrhoids might interfere with the accuracy of this screening tool. The direct answer is yes, active bleeding from hemorrhoids can indeed cause a positive FIT result, making it a frequent point of confusion for patients undergoing routine screening.
How the Fecal Immunochemical Test Works
The FIT test is a modern screening method that specifically targets human hemoglobin, which is the protein responsible for carrying oxygen in red blood cells. Unlike older tests that used chemical reactions, the FIT uses antibodies to bind to the globin component of human blood, making it highly specific to bleeding in the lower gastrointestinal tract, such as the colon and rectum. This specificity means the test is not affected by dietary sources of blood, like red meat, or by certain medications, eliminating the need for strict dietary restrictions before testing.
The test is quantitative, meaning it measures the actual concentration of hemoglobin in the stool sample, often expressed in micrograms of hemoglobin per gram of feces. A predefined cutoff level, such as 10 µg/g, determines whether the result is considered positive or negative, indicating the presence of occult, or non-visible, blood. Because the antibodies are designed to detect intact hemoglobin, the test is generally less sensitive to bleeding originating in the upper GI tract, where blood is more likely to be partially digested.
Hemorrhoids as a Source of Bleeding
Hemorrhoids are swollen veins located in the anus and lower rectum, a common condition that affects a large portion of the adult population. These veins are delicate and can easily become irritated, especially during bowel movements, which often causes them to bleed. This bleeding is typically minor, but it introduces human blood into the stool as it passes through the rectum.
Internal hemorrhoids, which occur inside the rectum, are particularly likely to cause bleeding that mixes with the fecal matter and contaminates the sample. This contamination, even from a small amount of blood, is frequently sufficient to surpass the sensitive detection threshold of the FIT. Therefore, hemorrhoids are a plausible and common source of what is known as a false-positive result in the context of cancer screening.
Interpreting a Positive Result When Hemorrhoids Are Present
A positive FIT result simply signifies that human blood has been detected in the stool sample, confirming bleeding in the lower digestive system. The test cannot distinguish the source of the bleeding, meaning it cannot differentiate between blood from a cancerous lesion, a precancerous polyp, or a benign hemorrhoid. Active bleeding from hemorrhoids is a documented cause of a positive FIT result, often leading to a false-positive for colorectal cancer.
Even if a patient has a known history of hemorrhoids, the positive FIT result must be treated as a signal requiring further investigation. Relying on hemorrhoids to explain the blood could mean missing an underlying, more serious condition. Although research shows that many positive FIT cases do not involve advanced colorectal neoplasia, the presence of blood still warrants attention.
A positive result indicates an elevated level of blood in the stool compared to the test’s cutoff, demanding definitive follow-up to locate the source. The primary goal remains ruling out polyps or cancer, as these serious conditions can coexist with hemorrhoids. The sensitivity of the FIT means that even minimal bleeding can trigger a positive outcome.
Next Steps Following a Positive FIT Test
Following a positive FIT result, the standard medical protocol is to proceed with a diagnostic colonoscopy. This is the only procedure that allows a physician to directly visualize the entire lining of the colon and rectum to accurately identify the origin of the bleeding. The colonoscopy is essential because it can rule out significant issues like colorectal cancer and advanced polyps.
Even if the patient assumes the positive result is due to known hemorrhoids, a colonoscopy is necessary to ensure the blood is not coming from a lesion located higher up in the colon. During the procedure, a gastroenterologist can remove precancerous polyps and take biopsies of suspicious areas, which aids in cancer prevention. Clinical guidelines recommend scheduling this follow-up promptly, ideally within a few months, to avoid diagnostic delays.