Yes, there is now an FDA-approved blood test for colorectal cancer screening. Called Shield, made by Guardant Health, it was approved in 2024 and detects colorectal cancer with about 83% accuracy. It’s a meaningful new option, but it comes with important limitations, especially when it comes to catching cancer early or finding precancerous growths before they become dangerous.
How the Shield Blood Test Works
The Shield test is a liquid biopsy. It analyzes a standard blood draw for fragments of DNA shed by colorectal cancer cells. If those DNA signals are present, the test flags a positive result, and a follow-up colonoscopy is recommended. The test is designed for adults aged 45 and older who are at average risk for colorectal cancer and have no symptoms.
In the clinical trial that led to FDA approval, Shield correctly identified cancer in 54 of 65 people who were confirmed to have colorectal cancer by colonoscopy. That 83% detection rate sounds strong, but the details matter. The test performed very differently depending on how advanced the cancer was. It caught nearly 100% of Stage II, III, and IV cancers but only 55% to 65% of Stage I cancers. That means it missed up to 45% of the earliest, most treatable cases.
The Biggest Limitation: Precancerous Polyps
The main reason colonoscopy is so effective isn’t just that it finds cancer. It finds and removes precancerous growths (called advanced adenomas) before they ever become cancer. This is where the blood test falls short. Shield detected only about 13% of advanced precancerous polyps found by colonoscopy. That means roughly 87% of precancerous growths went undetected.
The test also had a specificity of 90%, which means about 10% of people without cancer or precancerous growths received a false positive result, leading to an unnecessary colonoscopy. For context, stool-based screening tests like FIT (fecal immunochemical test) generally have higher specificity and better detection rates for advanced adenomas, though they require handling a stool sample, which some people avoid.
Where Blood Tests Fit Among Screening Options
The U.S. Preventive Services Task Force, which sets the most widely followed screening guidelines, does not currently include blood tests in its recommended colorectal cancer screening strategies. Its 2021 recommendation specifically notes that serum (blood) tests were excluded “because of the limited available evidence” and because other effective options already exist. Those recommended options include colonoscopy every 10 years, stool DNA tests every 1 to 3 years, and FIT every year, starting at age 45.
So why does the blood test matter? Because roughly a third of eligible adults in the U.S. are not up to date on colorectal cancer screening. Many people skip screening because they find stool tests unpleasant or dread the colonoscopy prep. A simple blood draw during a routine doctor’s visit removes those barriers. The thinking behind Shield’s approval is that a less sensitive test someone actually completes is more valuable than a more sensitive test they avoid entirely.
What About CEA Blood Tests?
If you’ve heard of a blood test called CEA (carcinoembryonic antigen), that’s a different tool with a different purpose. CEA is not used for screening or diagnosing colorectal cancer. Many cancers that raise CEA levels don’t always do so, and plenty of non-cancerous conditions (liver disease, digestive problems, lung conditions) can push CEA levels up, making it unreliable as a screening tool.
CEA testing is used after a colorectal cancer diagnosis. Doctors order it before treatment to establish a baseline, during treatment to gauge whether therapy is working, and after treatment to watch for recurrence. A rising CEA level in someone previously treated for colorectal cancer can be an early signal that the disease has returned. But for someone who hasn’t been diagnosed, a CEA test tells you very little.
Medicare Coverage and Cost
Medicare covers the Shield blood test once every three years if you meet all of the following criteria: you’re between 45 and 85, you have no symptoms of colorectal disease (such as blood in your stool or lower GI pain), and you’re at average risk. Average risk means no personal history of polyps, colorectal cancer, or inflammatory bowel disease, and no family history of colorectal cancer, adenomatous polyps, or hereditary colorectal cancer syndromes.
If you have a family history or personal risk factors, the blood test isn’t covered by Medicare, and your doctor will likely recommend a colonoscopy or another more sensitive screening method instead. Private insurance coverage varies and is still catching up to the FDA approval.
Multi-Cancer Blood Tests
You may also have seen headlines about blood tests that screen for dozens of cancers at once, including colorectal cancer. These multi-cancer early detection tests, such as the Galleri test, look for DNA fragments from many cancer types in a single blood sample. None of these tests have received FDA approval yet, though some are available as lab-developed tests that doctors can order. They are not substitutes for standard colorectal cancer screening, and most guidelines do not recommend them for routine use at this point.
What This Means for You
If you’re 45 or older and have been putting off colorectal cancer screening, the Shield blood test gives you a new, genuinely easy option. A single blood draw every three years is far simpler than any other screening method available. But you should understand the tradeoff clearly: this test is much better at catching cancer that already exists than at catching the precancerous polyps that colonoscopy can find and remove. It misses nearly all of those early growths.
If you’re comfortable with a colonoscopy or a stool-based test, those remain more thorough options. If the choice is between a blood test and no screening at all, the blood test is a significant step forward. A positive result on any screening test, including the blood test, means a colonoscopy is the next step to confirm or rule out cancer.