Colon Cancer Screening Adds a Blood Test That Misses Polyps

Adrian Ford was 31, trained almost daily, and ate well when a mild ache in her abdomen sent her to the emergency room. She had no bleeding, no weight loss, and a routine checkup six months earlier had come back clean. The scan showed stage 4 colorectal cancer that had already spread to her liver. “I thought they had made a mistake and that this wasn’t my scan at all,” she told Newsweek after the diagnosis.

The American Cancer Society (ACS, the largest cancer nonprofit in the United States) updated its colorectal cancer screening guidelines on May 27, published in the journal CA: A Cancer Journal for Clinicians, and for the first time listed a blood test as an option. The society also ranked that blood test below colonoscopy and stool tests, because it catches only a small share of the precancerous growths that screening exists to remove.

What the Updated Guidelines Add to the Menu

The headline change is breadth. Adults at average risk are still told to begin screening at age 45 and continue through 75 when life expectancy is greater than 10 years, with screening generally discontinued past 85. What grew is the list of acceptable ways to do it.

Two at-home stool tests moved into the preferred tier. One is a refreshed multi-target stool DNA test, Cologuard Plus, and the other is a newer stool RNA test, ColoSense, both taken every three years. The genuinely new entry is a blood draw done in a doctor’s office, Guardant Health’s Shield test, approved by the US Food and Drug Administration (FDA, the federal medical-device regulator) in 2024 and covered by Medicare once every three years. It is the only addition the ACS declined to call preferred.

The split between preferred and reserve options is the whole story, and the table below shows where each method lands.

The recommendations apply only to people without symptoms and without elevated risk. Anyone with a personal or family history of the disease, advanced polyps, inflammatory bowel disease, or a hereditary syndrome falls outside the average-risk guidance, and so does anyone already experiencing bleeding or changes in bowel habits. For those patients, the advice is a colonoscopy, not a screening shortcut. The full guideline sits in the updated ACS colorectal screening recommendations published in CA.

Why the Timing Lands on Younger Patients

The expansion arrives against a worrying curve. Colorectal cancer used to read as a disease of older adults; the numbers no longer cooperate with that picture.

• 3% a year: the rise in colorectal cancer among people under 50 between 2013 and 2022, compared with a slower 0.4% annual climb in adults aged 50 to 64.
• About one third: the share of all colorectal cancers that are now rectal cancers, a category rising roughly 1% a year since 2018.
• 158,850 new cases: the ACS estimate for the United States in 2026, alongside about 55,000 deaths.
• Number one: colorectal cancer is now the leading cause of cancer death among men under 50 and the second among younger women.

The society lowered the recommended starting age from 50 to 45 back in 2018, but the youngest eligible adults have been slow to act. In 2023, only 37% of people aged 45 to 49 were up to date with screening, against 55% of those aged 50 to 54. Ford’s story, diagnosed with no symptoms and no family history, is the kind of case driving the urgency. More than 20 million Americans who are eligible to screen have not done so.

The Polyp Problem Blood Tests Cannot Solve

Convenience is the blood test’s strongest selling point and its deepest weakness. A vial of blood is easy to give. What it struggles to find is the growth that has not yet become cancer at all.

What the Numbers Show

In the ECLIPSE trial, the registrational study behind Shield, nearly 8,000 evaluable participants across more than 200 US centers took the blood test and a colonoscopy as the reference standard. The blood test detected 83.1% of colorectal cancers overall, with sensitivity reaching 100% for stages 2 through 4 but falling to 64.7% for stage 1. For advanced precancerous lesions, the figure collapsed to 13.2%. A competing blood test from Freenome, studied in the PREEMPT CRC trial and still under FDA review at publication, managed only 12.5% on the same measure. The headline results are laid out in the New England Journal of Medicine report on the cell-free DNA blood test.

Why Polyps Matter More Than Detection

That gap is not a footnote. Most colorectal cancers begin as polyps that grow slowly over years, and removing them during a colonoscopy stops the cancer before it starts. Modeling cited in the guideline attributes about 80% of the long-term benefit of screening to finding and removing those lesions, not to catching tumors that already exist. A test that misses roughly 87 of every 100 advanced precancerous lesions is, by design, a detector rather than a preventer.

Blood tests are not the first choice. There are many people who cannot or will not undergo colonoscopy, or who are not willing to collect a stool sample. More options may help more people get screened, detect cancer earlier and allow us to cure more patients.

That was Dr. William Dahut, the ACS chief scientific officer, explaining the reasoning to CNN. The society’s own framing is blunt: some screening is better than none, but the blood test belongs in reserve.

Where Stool DNA Tests Earned the Preferred Label

The other newcomers cleared a higher bar. Unlike the blood test, the molecular stool tests look for both blood and altered DNA or RNA shed into the stool, and they pick up far more of the early disease that matters.

ColoSense, studied in more than 14,000 participants, detected 94.4% of colorectal cancers against 77.8% for a standard fecal immunochemical test (FIT, the common at-home test that checks stool for hidden blood). It caught every stage 1 cancer in the sample, where FIT found about 71%, and it flagged 45.9% of advanced precancerous lesions versus 28.9% for FIT. Cologuard Plus, evaluated in more than 26,000 people, posted 93.9% sensitivity for cancer and 43.4% for advanced lesions.

The trade-off with the stool DNA and RNA tests is lower specificity, meaning more false positives and more follow-up colonoscopies among people who turn out to be healthy. That is a cost the guideline accepts, because the tests still catch enough early disease to keep their preferred status. The blood test does not clear that threshold.

The Case for Adding a Weaker Test Anyway

So why list it at all? Because the most accurate test in the world prevents nothing if the patient never takes it, and a large share of eligible adults never do.

The Adherence Argument

Guardant Health told CNN that more than 90% of people complete screening when offered a blood test, against a range of 28% to 71% for colonoscopy or stool methods. Surveys cited in the guideline point the same way: 53% of respondents preferred a blood test every three years, 32% chose annual stool testing, and only 16% picked a colonoscopy every 10 years. The logic the authors lean on is simple, that the best screening test is the one a patient actually finishes.

The Catch in the Convenience

Dr. Shira Shor, a gastroenterologist at Maccabi Healthcare Services, draws the line that the marketing tends to blur. Blood tests are built to spot cancer that is already there, she notes, not to head it off. “This is one of the few cancers that can truly be prevented,” she said, pointing to polyp removal as the step that does the preventing. Three caveats follow the blood test wherever it goes:

1. Real-world data on long-term adherence remain thin, including how many people actually repeat the test every three years.
2. Follow-up rates after a positive result are not yet well measured outside trials.
3. Any positive result from a blood or stool test still demands a follow-up colonoscopy, ideally within six months.

If the blood test pulls reluctant patients into screening who would otherwise skip it entirely, it adds protection the system did not have. If it instead nudges people away from colonoscopies and stool tests they would have completed, it trades prevention for convenience, and the youngest patients, the ones whose numbers are climbing fastest, are the ones with the most to lose from that swap.

Frequently Asked Questions

At what age should I start colorectal cancer screening?

Age 45 for adults at average risk, according to the updated ACS guideline. Screening continues through age 75 for people with a life expectancy greater than 10 years, becomes an individual decision between 76 and 85, and is generally discontinued after 85. People with a family history or other risk factors may need to start earlier.

Is the blood test as good as a colonoscopy?

No. The Shield blood test detected 83.1% of colorectal cancers in the ECLIPSE trial but only 13.2% of advanced precancerous lesions, while colonoscopy both finds and removes those growths in the same procedure. The ACS ranks colonoscopy as the gold standard and lists the blood test as a reserve option only.

What is the Shield blood test and how often can I take it?

Shield, made by Guardant Health, is a blood draw done in a doctor’s office that detects fragments of tumor-derived DNA circulating in the blood. It was approved by the FDA in 2024 and is covered by Medicare once every three years.

Why are colorectal cancer cases rising in young adults?

Researchers do not fully know. Incidence among people under 50 rose about 3% a year between 2013 and 2022, often in patients with no family history or symptoms. Colorectal cancer is now the leading cause of cancer death among men under 50 in the United States.

What happens if my blood or stool test comes back positive?

A positive result from any non-colonoscopy test requires a follow-up colonoscopy, ideally within six months. These tests screen for signs of disease; a colonoscopy is needed to confirm findings and remove any polyps.

Which screening tests does the ACS now prefer?

Colonoscopy every 10 years, CT colonography every five years, flexible sigmoidoscopy every five years, annual FIT or high-sensitivity stool blood tests, and the stool DNA and RNA tests Cologuard Plus and ColoSense every three years. The blood test sits outside this preferred group.

Disclaimer: This article is for informational purposes only and is not medical advice. Cancer screening decisions depend on individual risk factors, age, and health history, and you should consult a qualified physician before choosing or skipping any screening method. Figures and guideline details are accurate as of publication on May 29, 2026.