Cologuard is a non-invasive screening test designed to detect signs of colorectal cancer or precancerous growths. It offers an at-home option for individuals at average risk for colorectal cancer, providing a convenient method for early detection. The test identifies specific indicators in stool samples that may suggest the presence of abnormal cells within the colon or rectum. Its purpose is to serve as a screening tool, helping to identify individuals who may require further diagnostic evaluation.
How Cologuard Works
Cologuard analyzes a stool sample for specific biological markers associated with colorectal cancer and precancerous polyps. The test identifies altered DNA biomarkers shed from cells lining the colon and rectum into the stool. These DNA changes can indicate the presence of cancerous or precancerous growths.
Cologuard also tests for occult (hidden) blood in the stool, specifically human hemoglobin. The presence of blood can indicate abnormalities within the digestive tract, as both cancers and polyps can sometimes bleed. This combined approach of DNA and blood marker detection enhances the test’s ability to identify potential concerns.
Interpreting a Positive Cologuard Result
A positive Cologuard result indicates the detection of abnormal DNA or blood in the stool sample. It suggests the presence of abnormal cells that could be associated with precancerous polyps or colorectal cancer. However, a positive result does not definitively mean cancer is present.
Clinical studies show that approximately 3% to 4% of individuals with a positive Cologuard test are found to have colorectal cancer upon subsequent colonoscopy. This means the majority of positive Cologuard results do not indicate cancer.
Understanding False Positives and Other Findings
A positive Cologuard result may not always signify cancer, partly due to false positives. A false positive occurs when the test indicates an abnormality, but a follow-up colonoscopy reveals no cancer or significant precancerous condition. The false positive rate for Cologuard ranges from 13% to 14%.
Various non-cancerous conditions can also lead to a positive Cologuard result. The test can detect DNA from non-cancerous polyps, which are benign growths in the colon. Other gastrointestinal issues, such as hemorrhoids, diverticulitis, or inflammation, can cause blood in the stool, leading to a positive result.
What Happens After a Positive Test
Following a positive Cologuard test, a diagnostic colonoscopy is the next step. This procedure allows a gastroenterologist to visually examine the entire colon and rectum for polyps, abnormalities, or signs of cancer.
During a colonoscopy, suspicious growths like polyps can be removed. Tissue samples (biopsies) can also be taken for laboratory analysis to determine if cancer or precancerous cells are present. This procedure is important for accurate diagnosis and early treatment of any identified conditions.