Adults 45–75
USPSTF recommends colorectal cancer screening from ages 45 to 75. The best method is the one you can complete with appropriate follow-up.
Evidence-led screening guide
Blood Test for Colon Cancer: What Each Option Does
Blood tests can make screening easier, but they do not replace colonoscopy or stool testing. This guide compares what each option can—and cannot—tell you.
Compare screening optionsClinical review status
Pending physician review. A named MD has not yet been supplied; no medical reviewer is represented in the page schema.
The short answer
Can a Blood Test Detect Colon Cancer?
Yes, for some people. Shield from Guardant Health is FDA-approved to screen for colorectal cancer. Galleri®, a multi-cancer blood test, screens for a signal shared by more than 50 cancer types, including colon and rectal cancer; it is under FDA review and is not FDA-approved or cleared. Neither replaces colonoscopy or guideline-recommended screening.
These tests analyze cell-free DNA (cfDNA)—small DNA fragments circulating in blood—for cancer-associated patterns. They answer different questions: Shield is colorectal-cancer-specific, while Galleri is multi-cancer.
Start with the screening comparison, or jump to how Shield and Galleri differ. See all cancers the Galleri test screens for.
One blood draw, different signals
How Blood Tests for Colon Cancer Work
Blood tests analyze a sample for DNA fragments shed into the bloodstream. Shield looks for alterations associated with colorectal cancer. Galleri analyzes methylation patterns shared by many cancers. Neither requires bowel prep, fasting or sedation.
The central limitation
Blood tests do not find and remove precancerous polyps. A convenient blood draw is not equivalent to a colonoscopy.
Side-by-side
Comparison: Colonoscopy vs Stool Tests vs Blood Tests
Each option finds different things. Colonoscopy is the most sensitive and the only option that can remove polyps. Stool tests are completed at home. Blood tests ask less of the patient but find fewer cancers and few or no polyps.
| Feature | Colonoscopy | Shield (blood) | Galleri (blood) | Cologuard (stool DNA) | FIT (stool) |
|---|---|---|---|---|---|
| What it screens for | Colorectal cancer; finds and removes polyps | Colorectal cancer only | A signal shared by 50+ cancer types, including colon/rectum | Colorectal cancer and advanced polyps | Blood in stool |
| CRC sensitivity | About 95% | 83.1% (ECLIPSE, 2024) | Not established prospectively for CRC | About 92% (NEJM, 2014) | About 74% |
| Finds precancerous polyps? | Yes—and removes them | Rarely; 13.2% advanced adenoma sensitivity | No | Some | No |
| Specificity | About 95% | 89.6% | 99.6% across all cancers in PATHFINDER 2 | About 87% | About 96% |
| Regulatory status | Established standard of care | FDA-approved (July 2024) | Under FDA review; not FDA-approved or cleared | FDA-approved | FDA-cleared |
| Guideline status | USPSTF-recommended option | Not included in the 2021 USPSTF recommendation | No USPSTF, ACS or NCCN endorsement | Included in guidelines | Included in guidelines |
| Insurance | Typically covered as preventive screening | Varies; check your plan | Not covered by Medicare; self-pay | Usually covered for eligible adults | Usually covered for eligible adults |
| Preparation | Bowel prep and sedation | Blood draw | Blood draw | Stool sample at home | Stool sample at home |
| If positive | Biopsy or removal during procedure | Colonoscopy | Diagnostic workup; imaging, then colonoscopy where indicated | Colonoscopy | Colonoscopy |
Figures are population-level study estimates, not a prediction for one person. Shield figures are from ECLIPSE (NEJM, 2024); Galleri specificity is across all cancers in PATHFINDER 2, not CRC-specific. No prospectively validated Galleri CRC sensitivity is available.
Prospective evidence first
How Accurate Is Galleri for Colon Cancer?
PATHFINDER 2 followed 35,878 adults age 50 or older. In full results, Galleri found 69.8% of cancers in GRAIL’s pre-specified group of 12—which includes colon/rectum—and 39.3% across all cancers. These are group results, not CRC-specific sensitivity.
69.8%Episode sensitivity for the pre-specified 12-cancer group
39.3%Episode sensitivity across all cancers
99.6%Specificity across all cancers
Positive predictive value was 60.3%. The May 2026 full results supersede the interim ESMO 2025 headline figures. A “No Cancer Signal Detected” result does not rule out cancer.
NHS-Galleri produced mixed results: its primary endpoint—a reduction in combined stage III–IV diagnoses across the 12 cancers—was not met, while stage IV diagnoses fell by more than 20% in rounds two and three.
Evidence note: the brief’s 82% colon/rectum case-control figure remains unavailable pending verification against the primary study figure and is intentionally not presented as a performance claim.
If colon cancer is your specific concern, colonoscopy remains the most sensitive option. Galleri adds a multi-cancer signal from one blood draw; it is not a substitute. Read the broader Galleri evidence and limitations.
The trust-critical limitation
What Blood Tests Cannot Do
No blood test finds and removes precancerous polyps. Colonoscopy is the only screening method that can do both in one procedure.
False negatives occur. A normal blood-test result does not rule out cancer, and symptoms still need prompt diagnostic evaluation.
Galleri does not replace colonoscopy, stool testing or any screening recommended for your age and risk. A “Cancer Signal Detected” result requires diagnostic workup.
One cancer versus more than 50
Shield and Galleri: Two Different Blood Tests
Shield asks whether there is a colorectal cancer signal in the blood. Galleri asks whether there is a cancer-associated signal shared by any of more than 50 cancer types. They have different jobs and regulatory statuses, so one does not substitute for the other. Human Longevity sells Galleri.
Eligibility and next steps
Who Should Consider a Blood Test for Colon Cancer?
Blood-based screening may be an option for eligible adults who are not completing recommended colorectal screening because of access, bowel-prep concerns or preference. It is not the first choice over colonoscopy for most people.
Elevated cancer risk
Galleri is physician-ordered and recommended for adults with elevated cancer risk, such as those 50 or older. It is not recommended during pregnancy, at age 21 or younger, or during active cancer treatment.
Symptoms or high risk
Rectal bleeding, a persistent bowel-habit change, iron-deficiency anemia, or a significant family history may call for diagnostic colonoscopy rather than a blood screening test.
Price and coverage
Cost and Insurance
Colonoscopy and stool tests are typically covered as preventive screening for eligible adults. Galleri costs $798 through Human Longevity, is HSA/FSA eligible, and is not covered by Medicare or most insurance. Shield coverage varies by plan; check with your insurer.
The MCED Screening Coverage Act was signed on February 3, 2026, but possible Medicare coverage from 2028 would still depend on FDA approval and a CMS coverage decision.
Galleri cost and coverageRegulatory status · October 7, 2026
Regulatory Status of Each Test
Colonoscopy is the established standard of care. Shield was FDA-approved in July 2024. Galleri is under FDA review: GRAIL filed a premarket approval application on January 29, 2026, and an FDA advisory panel voted on September 23, 2026 that benefits outweigh risks (7–2, one abstention) and 6–4 that it is effective.
The vote is non-binding. No FDA decision has been issued, and Galleri has not been approved or cleared.
Read the current Galleri FDA statusClear answers
FAQ
Is a blood test as good as a colonoscopy for colon cancer?
No. Colonoscopy is the most sensitive screening option and can find and remove precancerous polyps in the same procedure. Blood tests find fewer cancers and do not remove polyps.
What is the Shield blood test?
Shield is an FDA-approved blood test from Guardant Health that screens specifically for colorectal cancer. A positive result requires a follow-up colonoscopy.
Does Galleri detect colon cancer?
Galleri is not a colon-cancer-specific test. It screens for a signal shared by more than 50 cancer types, including colon and rectal cancer, and does not replace colonoscopy. A “No Cancer Signal Detected” result does not rule out cancer.
How much does a colon cancer blood test cost?
Galleri costs $798 through Human Longevity and is not covered by Medicare. Shield coverage varies by plan. Colonoscopy and stool tests are typically covered as preventive screening for eligible adults.
Can a regular blood test detect colon cancer?
No. A standard complete blood count or metabolic panel does not screen for colon cancer. Specialized DNA-based tests such as Shield and Galleri are different from routine bloodwork.
Inherited risk is a different question
Where Whole Genome Sequencing Fits
Whole genome sequencing does not screen for an existing colon cancer. It may identify inherited risk that changes when screening should begin or how often it should occur.
A strong family history or a relative diagnosed young can be a reason to discuss hereditary syndromes such as Lynch syndrome. A clear genetic result does not reduce the need for age-appropriate screening because most colorectal cancers are not explained by one inherited variant.
Read about Lynch syndrome and inherited colorectal cancer risk, or see what the $599 genome service includes. Galleri, WGS and guideline screening answer different questions; none replaces the others.
Sources and Evidence Notes
Key sources: USPSTF colorectal cancer screening recommendation (2021); Imperiale et al., New England Journal of Medicine (2014, stool DNA); Chung et al., New England Journal of Medicine (2024, ECLIPSE); GRAIL PATHFINDER 2 full-results release (May 31, 2026); GRAIL NHS-Galleri release (2026); FDA advisory committee materials (September 23, 2026); and Centers for Medicare & Medicaid Services coverage information. Study percentages describe populations, not an individual outcome.