Should you choose a blood test for colorectal cancer screening?

A blood test for colorectal cancer screening is now an option in the United States. But for most average-risk adults who are willing to do an at-home stool test or get a colonoscopy, it is still not the usual best first choice.

What changed is this: on May 27, 2026, the American Cancer Society updated its colorectal cancer screening guideline and added a blood-based option. At the same time, it kept stool-based and direct-visualization tests as the preferred strategies for average-risk adults. In plain language, the update means a blood test may be a reasonable fallback if the alternative is skipping screening altogether. It does not mean blood testing has replaced colonoscopy or recommended stool testing.

What changed in the new guideline

The main age guidance did not change. The American Cancer Society still says average-risk adults should start colorectal cancer screening at age 45. Routine screening is still advised through age 75 for people with a life expectancy of more than 10 years, while decisions from ages 76 to 85 should be individualized. People older than 85 generally should not continue screening.

The new part is that the guideline now includes a doctor-ordered blood test done in a healthcare setting. But the group also says blood-based screening should be used only for people who decline or do not complete preferred screening tests.

Who this blood test is for — and who it is not for

The FDA-cleared blood test, Shield, is intended for adults 45 and older who are at average risk for colorectal cancer and need screening. It is not a replacement for diagnostic colonoscopy, and it is not meant for people who need surveillance because they are already in a higher-risk group.

That matters because screening is for people without symptoms. If you have blood in the stool, ongoing lower abdominal pain, unexplained iron-deficiency anemia, a recent positive stool test, or another concerning change in bowel habits, you should not assume a screening blood test is the right next step. The same is true if you have a personal history of colon polyps or colorectal cancer, inflammatory bowel disease, or a strong family or hereditary risk. In those situations, a clinician may recommend direct evaluation, often with colonoscopy.

Seek prompt medical care for severe abdominal pain, black or tarry stools, heavy rectal bleeding, or symptoms of bowel blockage such as vomiting and inability to pass stool or gas.

How well does the blood test work?

The headline number many readers will hear is that the test detected colorectal cancer about 83% of the time in its pivotal study. That sounds promising, and it is one reason the test is now part of the conversation.

But the more important limitation is what it misses before cancer is fully established. In the prospective study behind the test, which included 7,861 adults already scheduled for screening colonoscopy, the blood test detected advanced precancerous lesions only 13.2% of the time. Detection was also lower for stage I cancers than for later stages. That is a major reason the American Cancer Society did not move blood testing into its preferred first-line group.

Why does that matter? Good screening ideally finds high-risk growths early enough to remove them or catch cancer at the earliest possible stage. A test that is much weaker at finding advanced precancerous lesions may detect some cancers that are already present, but it is less helpful for prevention.

The FDA also notes that about 1 in 10 people who do not have advanced abnormal cells will still have a false-positive Shield result. And a negative test does not guarantee that cancer is not present.

Why stool tests and colonoscopy still matter

For most average-risk adults, the stronger screening value still comes from established options such as annual FIT, stool DNA-FIT every 1 to 3 years, CT colonography, flexible sigmoidoscopy, or colonoscopy every 10 years. The U.S. Preventive Services Task Force, whose recommendations carry major insurance implications, still does not include serum tests in its current colorectal screening recommendation because evidence is limited and other effective tests already exist.

Colonoscopy has one clear advantage a blood test does not: it can find and remove precancerous polyps during the same procedure. That means it can help prevent cancer, not just look for signs that cancer may already be there. Stool tests are also indirect tests, but they remain part of well-established screening strategies with more evidence behind them.

If the blood test is positive, screening is not finished

A positive blood test does not diagnose colorectal cancer by itself. It means you still need a follow-up colonoscopy. The American Cancer Society says a positive stool or blood screening result should be followed by timely colonoscopy, preferably within 6 months, to complete the screening process.

This is one of the most important practical questions to ask before choosing the blood test: if it comes back positive, are you willing and able to get a colonoscopy? If the answer is no, the blood test may not solve the main barrier.

What Medicare covers, and why private insurance may vary

For Medicare beneficiaries, the rules are relatively clear. Medicare Part B covers blood-based biomarker colorectal screening once every 3 years for eligible adults ages 45 to 85 who are at average risk and have no symptoms. Medicare says you pay nothing if your provider accepts assignment, and it also covers a follow-up colonoscopy after a positive blood-based screening result.

Private insurance is less straightforward right now. Under the Affordable Care Act, many private plans must cover U.S. Preventive Services Task Force-recommended colorectal screening tests without out-of-pocket costs when used appropriately. But the current USPSTF recommendation does not include serum tests. Some plans may still cover a blood-based test, but readers should not assume it will automatically be treated the same way as no-cost preventive FIT or colonoscopy. Coverage can vary by insurer, employer plan, network status, and whether the test is ordered in a way the plan recognizes as covered preventive screening.

Before ordering a blood test, ask your plan these questions: Is this specific test covered? Is it considered preventive screening? Is the lab in network? And if the result is positive, how will the follow-up colonoscopy be covered?

So when is a blood test a reasonable choice?

For an average-risk adult who has kept putting off screening, a blood test may be a reasonable backup option if it helps get screening started. That is the most practical takeaway from the guideline update.

But if you are willing to do annual FIT, another recommended stool test, or colonoscopy, those options still offer more proven screening value. They remain the better first conversation for most people because they fit established screening pathways and, in the case of colonoscopy, can also prevent cancer by removing precancerous growths.

Bottom line

The new American Cancer Society guideline did not make blood testing the new standard choice for most average-risk adults. It added a new option for people who decline or do not complete preferred tests. If a blood test is the option you will actually complete, it may be better than no screening. But if you are choosing among tests from the start, stool testing and colonoscopy still have the stronger track record for colorectal cancer screening and prevention.

Sources

Editorial note: Weence articles are researched from cited public-health, medical, regulatory, journal, and reputable news sources and may be drafted with AI assistance. They are checked for source support, clarity, and safety guardrails before publication.

This article is for general informational purposes only and is not medical advice. Research findings can be early or incomplete, and health guidance can change. Always talk with a qualified healthcare professional about personal symptoms, diagnosis, medications, vaccines, screenings, or treatment decisions. If you think you may have a medical emergency, call emergency services right away.