Cologuard is a at-home stool test that screens for colorectal cancer and precancerous growths by analyzing your stool for abnormal DNA and hidden blood. It’s one of several FDA-approved screening options for adults at average risk of colorectal cancer, and the only multitarget stool DNA test currently on the market.
The Three Biomarkers Cologuard Detects
Cologuard doesn’t look for just one thing. It targets three distinct categories of biomarkers, each tied to the development of colorectal cancer or precancerous polyps.
The first category involves changes to how certain genes are switched on or off. When cells become cancerous, they sometimes silence genes that would normally suppress tumor growth. Cologuard looks for this silencing pattern in two specific genes. These changes show up early in the process, sometimes before a polyp becomes cancerous.
The second category involves mutations in a gene that controls cell growth signals. When this gene mutates, it can trigger cells to multiply uncontrollably, a hallmark of cancer development. Cologuard scans your stool DNA for specific point mutations in this gene.
The third category isn’t DNA-based at all. It detects hemoglobin, the protein in red blood cells, which signals bleeding somewhere in the colon or rectum. Cancerous and precancerous growths often bleed in small amounts you’d never notice on your own. This component works similarly to a standard fecal immunochemical test (FIT), which many doctors use as a standalone screening tool.
By combining all three categories, Cologuard catches abnormalities that any single marker might miss.
How Accurate Is Cologuard?
Cologuard detects colorectal cancer with about 92% sensitivity, meaning it catches roughly 92 out of every 100 cancers present. Its specificity sits around 87%, which means about 13 out of every 100 people without cancer or advanced polyps will get a positive result anyway.
Where Cologuard falls short is with precancerous growths. Its sensitivity for advanced adenomas, the larger polyps most likely to become cancer, is only about 42%. That means it misses more than half of these precancerous polyps. This is a real limitation. Colonoscopy, by comparison, can both detect and remove polyps in the same procedure, which is why it remains the gold standard for prevention, not just detection.
A standard FIT test also detects hidden blood in stool but doesn’t analyze DNA. FIT has comparable cancer detection rates but is less expensive. Cologuard’s DNA analysis gives it a slight edge for catching some cancers that aren’t bleeding, but both tests miss a significant number of precancerous polyps.
Who Should Use Cologuard
The U.S. Preventive Services Task Force recommends colorectal cancer screening for all adults starting at age 45, with the strongest recommendation for those aged 50 to 75. Adults 76 to 85 can discuss screening with their doctor based on individual health and screening history.
Cologuard is designed for people at average risk. That means no prior diagnosis of colorectal cancer, adenomatous polyps, or inflammatory bowel disease, and no personal or family history of genetic conditions like Lynch syndrome or familial adenomatous polyposis that dramatically increase colorectal cancer risk. If any of those apply to you, colonoscopy is typically the recommended approach because it offers direct visualization and the ability to remove suspicious tissue immediately.
How Often You Need to Repeat It
The recommended screening interval for Cologuard is every one to three years. That’s more frequent than colonoscopy, which is recommended every ten years for average-risk adults with normal results. The tradeoff is straightforward: Cologuard is less invasive and requires no prep or sedation, but you’ll need to repeat it far more often to maintain reliable screening coverage.
What Happens With a Positive Result
A positive Cologuard result does not mean you have cancer. It means the test found abnormal DNA markers or blood that need further investigation. The next step is a diagnostic colonoscopy, which is the only way to determine what caused the abnormal result. Most doctors recommend scheduling this within a few months of the positive test.
Given that roughly 13% of people without cancer or significant polyps will still get a positive result, a fair number of follow-up colonoscopies will find nothing concerning. That can feel frustrating, but it’s a built-in feature of any screening test sensitive enough to catch real cancers. The alternative, missing a cancer that could have been caught early, carries far greater consequences.
How the Test Works at Home
Cologuard arrives as a kit shipped to your home. You collect a stool sample using the provided container, no special diet or bowel prep required. After collection, you ship the sample back to the lab using a prepaid shipping box. The lab analyzes the DNA markers and hemoglobin levels and sends results to your doctor, who contacts you with the findings. The entire process, from collection to results, typically takes a couple of weeks.