Colon Cancer Screening with a Blood Test: Are Colonoscopies Over?
Blood tests for colon cancer screening are making headlines — but the science says they are not ready yet to replace colonoscopy. Here is exactly why, with no spin.
Serological tests look for tumour signals in the blood. Promising — but with important limitations for population-based screening.
TL;DR — The quick version
What exists:
- • Blood tests that detect colon cancer signals, with encouraging lab results.
- • Some are already approved in the US for specific situations (not for the general population).
- • Research is moving fast.
What is still missing:
- • Sensitivity is too low to detect advanced polyps (the ones that matter most to prevent).
- • No validation in large, long-term population studies yet.
- • Colonoscopy remains the reference method for real screening.
Colon cancer screening with a blood test is probably one of the questions I get most often in clinic: "Doctor, can't I just have a blood test instead of a colonoscopy?" I completely understand. Colonoscopy feels like a big deal — you need to prepare, take a day off work, and it is not exactly anyone's idea of fun. But before we take the easy route, let us look at what the science actually says today — not the newspaper headline, the real data.
Quick navigation
- • What are serological tests for colon cancer?
- • Types of biomarkers: proteins, DNA and antibodies
- • What the science actually says (real numbers)
- • The big problem: detecting polyps, not just cancer
- • What are these tests actually useful for today?
- • So, is colonoscopy dead? (Spoiler: no.)
- • Frequently asked questions
What are serological tests for colon cancer?
Think of it this way: when something goes wrong inside your body, it leaves clues — like breadcrumbs — in the bloodstream. That is essentially what these tests look for. A serological test is any blood analysis that searches for specific biomarkers that could signal the presence of a tumour. It does not look directly at the colon; instead, it picks up on what that tumour leaves behind in the circulation.
The appeal is huge: you give a blood sample, go home, and wait for the result. No prep, no sedation, no day off. That makes people far more willing to do it. And in screening, participation is everything — the best test in the world is useless if nobody does it. 1
Types of biomarkers being investigated
Not all blood tests look for the same thing. Here are the three main categories researchers are working with:
Cell-free DNA (cfDNA)
Fragments of tumour DNA circulating in the blood. The most talked-about is the Shield test (cfDNA), published in the NEJM in 2024.
Tumour proteins
Markers like CEA, CYFRA21-1, CA19-9 or novel proteins such as COL10A1. Several studies combine 5–8 markers to improve accuracy.
DNA methylation
Chemical changes in specific genes (GALNT9, WARS, LDB2…) that appear in serum when cancer or advanced adenoma is present.
Autoantibody panels, AI-assisted spectroscopic analysis, and multi-marker combinations are also being explored to try to push sensitivity higher. 23
What the science actually says (real numbers, no hype)
Here is the part that matters. I am going to walk you through the studies that have genuinely moved this field forward — without translating the results into "medical revolution" headlines that never quite arrive.
The Shield Test (cfDNA) — NEJM 2024
This is the test that generated the most buzz. Published in the New England Journal of Medicine, 4 the Shield test analyses cell-free tumour DNA in blood. For detecting established colorectal cancer, the numbers are striking: 83% sensitivity. That sounds great. But for real screening, you need to catch advanced polyps — the pre-cancerous stage — before they turn into cancer. There, sensitivity drops to 13–14%. That is simply not good enough.
Multi-protein panels
Several research groups have worked with combinations of 5 to 8 blood proteins. Werner and Brenner (2015) 5 tested a 5-marker panel in a real screening setting and got moderate — but insufficient — results. Wilhelmsen et al. (2017) 2 combined 8 protein biomarkers. The takeaway: combining markers does improve things slightly compared to CEA alone, but still falls short for population screening.
A more recent cost-effectiveness analysis (Rui et al., 2025) 6 reported that the best combination of serum markers reached a sensitivity of 69.6% at 95% specificity. In plain language: with that test, nearly 1 in 3 cancers would be missed. That is not acceptable for a screening programme.
Serum methylation markers
A Spanish research team from CIBEREHD (Gallardo-Gómez et al., 2023) 3 published interesting data on methylated serum genes (GALNT9, UPF3A, WARS, LDB2) as potential biomarkers. They perform well in lab conditions, but still need validation in large clinical trials. Likewise, the protein panel by Chavany et al. (2025), 7 presented at the Journal of Clinical Oncology, shows promising early-detection results — but is still pending population-level confirmation.
The genuine upside: people actually do them
There is one area where these tests clearly win: people are far more willing to do a blood test than a colonoscopy or even a stool-based test. That can dramatically increase screening coverage, which in many countries is still disappointingly low. Goyal et al. (2025) 8 showed that annual blood tests are well accepted as a surveillance supplement. Note: supplement, not replacement.
The big problem: colon cancer starts as a polyp
This is the crux of the matter, and what makes the issue more complex than headlines suggest. Colorectal cancer does not appear out of nowhere: it starts as a polyp that grows and changes over years before becoming a tumour. Screening exists precisely to find that polyp before it becomes cancer and remove it. That is what saves lives.
The Achilles heel of serological tests
Current blood tests detect a formed cancer reasonably well, but they are very poor at detecting advanced adenomas — the polyps that are on the verge of becoming cancer. And that is precisely the stage screening needs to catch. Meester et al. (2025) 9 published a comparative analysis in the JNCI showing that current blood tests have a significantly lower capacity to prevent colorectal cancer deaths compared with colonoscopy or even a well-implemented faecal occult blood test (FOBT).
Rex et al. (2017), representing the consensus of the main US scientific societies on colorectal cancer screening, 10 made it clear in their guidelines that serological tests do not yet have sufficient evidence to be recommended as a first-line screening method. Those guidelines are constantly reviewed — if the evidence were there, they would have changed by now.
The economics have also been scrutinised carefully. Ladabaum et al. (2024), writing in Annals of Internal Medicine, 11 found that novel molecular blood tests can only be cost-effective if their sensitivity improves considerably over what we currently have.
Not sure which screening test is right for you? Let's talk through it properly in a consultation.
What are these tests actually useful for today?
Not being ready for screening does not mean they have no value. They do — just a different role:
-
1
Diagnosing established cancer
When symptoms or clinical suspicion are already present, these tests can help guide and support the diagnostic workup. Their 70–83% sensitivity for established cancer is clinically useful here.
-
2
Monitoring treatment response
In patients already diagnosed, markers like CEA or cfDNA panels help track response to treatment and detect relapse early.
-
3
Supplementary surveillance (not a substitute)
In high-risk patients or after polypectomy, they may be used as a complement between colonoscopies — never instead of them. 8
-
4
A nudge for reluctant patients
For patients who firmly refuse a colonoscopy, a positive blood test result could be the turning point that finally brings them in for the proper procedure. 12
So, is colonoscopy dead? Spoiler: no.
I am going to be straight with you: colonoscopy is not going anywhere in the next few years. And I am not saying that out of professional bias. I am saying it because it is the only test that can, in a single session, both find and remove a polyp before it becomes cancer. No blood test can do that yet.
What could happen — and is already being studied — is that in the future, blood tests act as a first filter: if the test is negative in a low-risk person, colonoscopy intervals could be extended. If positive, immediate colonoscopy. That model could improve screening coverage without overwhelming endoscopy units. But it still needs more evidence before becoming standard practice. 9
And when colonoscopy does find a complex polyp, the story does not end there — it needs to be treated. That is where advanced endoscopy techniques come in, solving most cases without surgery. For example, Endoscopic Mucosal Resection (EMR) for intermediate-sized polyps, or Endoscopic Submucosal Dissection (ESD) for larger or more complex lesions, allowing en-bloc resection with high precision. A blood test cannot do any of that.
Advanced Endoscopy
All available techniques explained →
Endoscopic Submucosal Dissection (ESD)
For complex and large polyps →
Endoscopic Mucosal Resection (EMR)
Minimally invasive technique →
The bottom line
Serological tests are a technology with genuine future potential, but in 2026 they are not validated for population-based colon cancer screening. They are useful for diagnosing established cancer and as a surveillance supplement — not as a replacement for colonoscopy. If you are due for screening, do not put it off: modern colonoscopy under sedation is far more comfortable than you imagine, and if a polyp is found, it can be dealt with right then and there.
A personal note
There is a lot of noise online about this topic. My job is to cut through that noise and give you information that actually helps you make good decisions. Down here in the operating theatre is where we deal with problems that prevention did not catch in time. Let's make sure we don't need to get that far.
In theatre, team ready. But the goal is that we never have to get here.
Frequently asked questions
Can colon cancer be detected with a blood test?
Current blood tests can detect established colorectal cancer with acceptable sensitivity (around 70–83%), but they are not validated for screening healthy, asymptomatic individuals. Colonoscopy remains the gold standard for genuine prevention.
What is a serological test for colon cancer?
It is a blood test looking for tumour signals: proteins, tumour DNA fragments (cfDNA), or DNA methylation changes. Non-invasive and easy to do, but current versions have major limitations for detecting pre-cancerous lesions.
Can a blood test replace a colonoscopy?
Not yet. Colonoscopy is the only test that detects AND removes polyps in the same procedure — before they become cancer. Current blood tests simply do not have that preventive power.
When might blood tests be ready for colon cancer screening?
Research is moving fast, and it is likely that in a few years we will have tests with better sensitivity for advanced polyps. Once validated in large population studies, the screening model will evolve. But we are not there yet.
Related posts you will find useful
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How Often Should You Get a Colonoscopy?
From what age and how frequently, based on your actual risk.
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Why Is Colon Cancer Rising in Young Adults?
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Read post →Scientific references
- Kleif J, et al. Early detection of colorectal neoplasia: application of a blood-based serological protein test. British Journal of Cancer (2022). doi:10.1038/s41416-022-01712-x
- Wilhelmsen M, et al. Detection of colorectal neoplasia: combination of eight blood-based protein biomarkers. International Journal of Cancer (2017). doi:10.1002/ijc.30558
- Gallardo-Gómez M, et al. Serum methylation of GALNT9, UPF3A, WARS, and LDB2 as noninvasive biomarkers. Clinical Epigenetics (2023). doi:10.1186/s13148-023-01570-1
- Chung DC, et al. A Cell-free DNA Blood-Based Test for Colorectal Cancer Screening. New England Journal of Medicine (2024). doi:10.1056/nejmoa2304714
- Werner S, Brenner H, et al. Evaluation of a 5-Marker Blood Test for Colorectal Cancer Early Detection. Clinical Cancer Research (2015). doi:10.1158/1078-0432.ccr-15-1268
- Rui M, Wang Y, You J. Novel non-invasive tests for colorectal cancer screening — a cost-effectiveness analysis. Cancer Epidemiology, Biomarkers & Prevention (2025). doi:10.1158/1055-9965.epi-24-1549
- Chavany C, et al. A protein-based blood panel test for the early detection of colorectal cancer. Journal of Clinical Oncology (2025). doi:10.1200/jco.2025.43.4_suppl.46
- Goyal R, et al. Annual Blood Tests Are an Acceptable Form of Surveillance to Supplement Colonoscopies. Digestive Diseases and Sciences (2025). doi:10.1007/s10620-025-08906-2
- Meester R, et al. Comparative benefits, burdens, and harms of emerging blood-based tests for colorectal cancer screening. JNCI Journal of the National Cancer Institute (2025). doi:10.1093/jnci/djaf277
- Rex DK, et al. Colorectal Cancer Screening: Recommendations for Physicians and Patients from the U.S. Multi-Society Task Force. Gastroenterology (2017). doi:10.1053/j.gastro.2017.05.013
- Ladabaum U, et al. Projected Impact and Cost-Effectiveness of Novel Molecular Blood-Based or Stool-Based Screening Tests. Annals of Internal Medicine (2024). doi:10.7326/annals-24-00910
- Sapienza M, Davis C, Boudes M. Navigating the evolving landscape of colorectal cancer screening. Oncology Reviews (2025). doi:10.3389/or.2025.1653617
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