The Cologuard test is a widely advertised, non-invasive method for screening individuals for colorectal cancer. This at-home option analyzes a stool sample for signs of disease, offering a convenient alternative to traditional procedures like a colonoscopy. Hemorrhoids are a common and benign source of bleeding in the lower gastrointestinal tract. A frequent question is whether this common condition can interfere with the sensitive screening test, leading to a misleading result. This article explores how Cologuard works, the nature of hemorrhoidal bleeding, and the impact of hemorrhoids on test results.
Understanding How Cologuard Detects Colon Cancer
Cologuard is a multi-target stool DNA test that uses a dual mechanism to screen for colorectal cancer and precancerous polyps. The test analyzes the collected stool sample for two primary indicators related to cellular changes in the colon.
DNA Markers
The first component detects specific, abnormal DNA markers shed by cancer cells and advanced polyps into the stool. The analysis quantifies DNA methylation markers, such as NDRG4 and BMP3, along with KRAS gene mutations. These DNA changes represent the genetic signature of the disease process. The test is highly sensitive to these genetic signals, which can indicate the presence of abnormal growths.
Occult Blood Detection
The second component screens for the presence of occult, or hidden, human hemoglobin in the stool. Hemoglobin is the protein found in red blood cells, and its presence indicates bleeding somewhere in the gastrointestinal tract. This dual approach of analyzing both abnormal DNA and blood provides a strong connection to potential colorectal cancer or advanced precancerous lesions.
The Nature of Hemorrhoidal Bleeding
Hemorrhoids are swollen veins located in the rectum and anus, similar to varicose veins. These clusters of blood vessels become inflamed and distended due to factors like chronic constipation or straining during bowel movements. The resulting friction or pressure can easily cause the delicate vessel walls to break, leading to bleeding.
Bleeding from hemorrhoids occurs low in the GI tract, near the end of the digestive process. This blood is often bright red because it has not been digested or altered by stomach acids or intestinal enzymes. Although this bleeding is benign and not related to cancer, the blood mixes with the stool sample.
The bleeding, even if minor, is a source of human hemoglobin within the stool. Since Cologuard is highly sensitive to the presence of blood cells, regardless of their origin, hemorrhoids are a potential factor in screening tests that look for blood in the stool.
Impact of Hemorrhoids on Cologuard Test Results
Hemorrhoidal bleeding can lead to a positive Cologuard test result. This happens because the test relies on detecting occult blood (hemoglobin) in the stool and cannot distinguish between blood from a cancerous lesion and blood from a benign source like a hemorrhoid. Since Cologuard combines DNA and hemoglobin analysis to generate a single outcome, a strong hemoglobin signal contributes to a positive result.
If the test registers positive primarily due to blood from a hemorrhoid, but no abnormal DNA markers are present, the result is a “false positive.” This means the test indicated a problem requiring follow-up, even though the underlying cause is not colorectal cancer or an advanced polyp. The false-positive rate for Cologuard is estimated to be around 13%, meaning roughly one in eight positive results may not correspond to actual cancer or advanced polyps upon further investigation.
The blood from a hemorrhoid elevates the overall risk score calculated by the test’s algorithm. Individuals with active hemorrhoidal bleeding, menstruation, or diarrhea should avoid taking the test until the bleeding has stopped. However, a person should not dismiss a positive Cologuard result, as the test could still be detecting abnormal DNA that warrants investigation.
Clinical Follow-Up After a Positive Cologuard Result
A positive result from the Cologuard screening test requires immediate and mandatory follow-up, regardless of a suspected benign cause like hemorrhoids. Cologuard is strictly a screening tool that identifies individuals who should undergo further diagnostic testing. It is not a diagnostic tool that can confirm or rule out cancer on its own.
The next step is a diagnostic colonoscopy, which is considered the gold standard for colorectal cancer detection. This procedure allows a gastroenterologist to visually examine the entire colon and rectum, identify the true source of the bleeding, and remove any polyps or lesions found.
Waiting or assuming the positive result was solely due to hemorrhoids is strongly discouraged. Delays in follow-up can significantly increase the risk of finding more advanced-stage disease if cancer is present.
The follow-up colonoscopy determines the true meaning of the positive screening result. If the colonoscopy is negative, the Cologuard result is confirmed as a false positive. Recent regulatory changes mandate that a follow-up colonoscopy after a positive stool-based test should be covered by insurance as part of preventive screening.