More than 50 million American adults who are due for colorectal cancer screening have never had it. That gap is the commercial and public-health backdrop for a change the American Cancer Society made on May 27, when its updated 2026 guidelines listed a blood test, Shield from Guardant Health, as a screening option.
The guideline, published in CA: A Cancer Journal for Clinicians, is the first major update since 2018. It keeps the start age at 45 for average-risk adults and runs screening through age 75 for people with a life expectancy beyond 10 years.
Recommended, but not preferred
The wording matters. Shield is on the list as a recommended test, not a preferred one. The society’s text reads: “New blood-based tests are also among the recommended tests, but they are not a preferred option at this time.”
Preferred options stay as they were: colonoscopy every 10 years, high-sensitivity stool tests, or CT colonography every five years. A new stool RNA test called ColoSense was added to the preferred stool group.
The society gives its reasons plainly. Blood tests are not preferred “primarily because of lower sensitivity for advanced precancerous lesions and stage I colorectal cancers,” and the best testing interval has not been settled. Shield picks up tumor DNA circulating in the blood. It finds cancer that has formed better than it finds the precancerous polyps a colonoscopy can remove on the spot. A positive Shield result is not a diagnosis, and it calls for a follow-up colonoscopy, ideally within six months.
The Colorectal Cancer Alliance put it bluntly: people should use a blood test only if they are unwilling to have a stool test or a visual exam.
Dr. William Wolf, the lead guideline author, framed the larger aim as getting colorectal cancer seen as “a highly preventable disease as much as a treatable one.”
Who pays
The FDA approved Shield in 2024. Medicare covers it every three years for beneficiaries 45 and older, though the three-year interval is an administrative choice rather than one backed by long-term outcome data.
Private insurance is murkier. The US Preventive Services Task Force has not given Shield an A or B rating, so the Affordable Care Act’s no-cost-sharing rule does not apply and some patients may pay out of pocket. Colonoscopy and the task force’s recommended stool tests do carry that protection. The task force is expected to revisit its recommendations to account for blood tests and newer stool tests, but no date has been announced.
Distribution
On the supply side, Guardant announced on March 10 that physicians can order Shield through Quest Diagnostics. Quest serves nearly 650,000 clinician and hospital accounts a year in the US, with about 2,000 patient service centers and roughly 6,000 in-office phlebotomists available for blood draws.
AmirAli Talasaz, Guardant’s co-CEO, said the Quest arrangement would help doctors offer “a quick, easier screening option patients are far more likely to complete.” The company says Shield produces a 93% screening adherence rate. Colorectal cancer is the second leading cause of cancer-related deaths in the US, and Guardant puts the five-year survival rate at 91 percent when it is caught early.
Patients weighing the test should check their coverage first, since Medicare’s three-year interval is settled while private plans vary. Anyone with a family history of colorectal cancer or polyps may qualify for screening that begins before 45, and should discuss it with a gastroenterologist.
Sources
- A Blood Test for Colorectal Cancer Is Now Included in Official Screening Guidelines, with Key Limitations Patients Should Know
- Guardant Health’s Shield Blood-based Screening Test for Colorectal Cancer Now Accessible Through National Test Ordering and Collection Network of Quest Diagnostics
