Cologuard is a non-invasive screening method for colorectal cancer, offering an alternative to traditional procedures for average-risk individuals aged 45 and older. This at-home test analyzes a stool sample for specific markers associated with neoplasia, the abnormal growth of cells that can lead to cancer. Receiving a positive result from any screening test can cause anxiety. The question often arises whether common, benign conditions like hemorrhoids can interfere with the test’s accuracy.
How Cologuard Detects Markers
The Cologuard test utilizes a multi-target approach, analyzing the stool sample for two distinct types of markers: molecular DNA and human hemoglobin. Cancerous and precancerous cells shed DNA into the stool, and the test is designed to detect abnormal genetic alterations. These alterations include mutations in the KRAS gene and specific methylation markers, such as NDRG4 and BMP3, which are linked to colorectal cancer development.
The second component involves a highly sensitive immunoassay to identify the presence of human hemoglobin, or blood, in the stool. Bleeding can occur when advanced polyps or tumors are present, and this blood may not be visible to the naked eye, leading to the term “occ ult” blood. The test is calibrated to detect minute traces of this blood protein, which serves as a general indicator of bleeding within the lower gastrointestinal tract.
Hemorrhoids and False Positive Potential
Hemorrhoids are swollen veins in the anus and rectum, and they are a common source of bleeding in the lower digestive tract. When a hemorrhoid bleeds, the resulting blood introduces human hemoglobin into the stool sample. Since Cologuard’s blood detection component is highly sensitive, it cannot differentiate the source of the hemoglobin. It will register the presence of blood from hemorrhoids just as it would blood from a potential tumor.
This introduction of benign blood can lead to a positive Cologuard result based solely on the hemoglobin component, even if the DNA markers associated with cancer are absent. The test is designed to flag any combination of elevated DNA markers or the presence of blood as a positive outcome. This scenario, where a positive result is triggered by a non-cancerous condition, is referred to as a false positive.
Clinical studies show that the overall false positive rate for Cologuard is around 13% for patients without colorectal cancer or advanced precancerous lesions. Hemorrhoids are recognized as one possible cause contributing to this percentage, along with other sources of lower GI bleeding. Because the test is primarily a screening tool, its high sensitivity means it is susceptible to interference from common, benign conditions like bleeding hemorrhoids.
Navigating a Positive Cologuard Result
A positive Cologuard result should always be viewed as an abnormal screening finding that requires definitive follow-up, regardless of whether a benign cause like hemorrhoids is suspected. Cologuard is not a diagnostic tool; it only indicates that markers associated with colorectal neoplasia were detected. Patients must resist the temptation to assume that their known hemorrhoids are the sole reason for the positive finding.
The next necessary step is a diagnostic colonoscopy, which is the gold standard for confirming or ruling out the presence of cancer or advanced polyps. A colonoscopy provides a physician with a visual examination of the entire colon and rectum, allowing for the immediate removal of any polyps and biopsy of any suspicious tissue. Studies show that even after a positive Cologuard result, approximately 68% of patients have either normal colonoscopy findings or only non-advanced polyps.
Delaying the follow-up colonoscopy after a positive result is strongly discouraged due to the risk of allowing an undiagnosed cancer to progress. Major medical guidelines recommend that a diagnostic colonoscopy be performed within three months, and no later than six months, of receiving a positive stool test result. The colonoscopy serves as the final step in the screening process to determine the true cause of the positive Cologuard result.