'Recommending Blood Tests for CRC Without Guardrails Risks Confusion'

 The American Cancer Society's (ACS) recent update on colorectal cancer screening aims to strike a careful balance on blood-based screening tests. On the one hand, it appropriately calls them non-preferred options. On the other, it now includes them among acceptable screening choices for average-risk adults under limited circumstances.

That combination is likely to create more confusion than clarity. The document contains appropriate scientific caution, but insufficient implementation discipline. It recognizes the limitations of blood-based tests yet does not give clinicians or health systems the tools needed to prevent those tests from drifting into routine first line use.

The problem is not subtle. Once a screening test appears in a major guideline, patients, clinicians, health systems, payers, and the media often interpret that inclusion as endorsement. In practice, many will not distinguish between "listed as an option" and "recommended on equal footing." That is why it is not enough for a guideline to say blood-based tests are non-preferred. If those tests are added to the screening menu, there must also be a practical framework for implementation that makes their role unmistakable.

Without that framework, the guideline risks being read as a green light. That would be especially concerning given the evidence summarized in the guideline itself. Blood-based colorectal cancer screening tests are included only because of their potential appeal to people who otherwise remain unscreened. But the same guideline makes clear that they perform less well than preferred options, especially where it matters most: detection of advanced precancerous lesions. Their sensitivity for advanced adenomas is far lower than stool-based tests and dramatically below colonoscopy. That limitation is not a technical footnote. It gets to the very purpose of colorectal cancer screening.

The most effective colorectal cancer screening strategies do more than detect existing cancer. They prevent cancer by identifying precursor lesions before malignancy develops. A test that performs poorly at finding those lesions is not simply a weaker version of screening; it delivers less of the preventive benefit that makes screening so valuable in the first place.

The ACS acknowledges this, noting that blood-based tests are expected to reduce colorectal cancer incidence and mortality less effectively than established options. That should have led to a stronger implementation message. Instead, the update leaves a large operational gap. It says these tests should be used only for patients who decline or do not complete preferred screening.

But what does that mean in practice? How many outreach attempts should occur first? Which preferred tests should be offered before blood testing is introduced? How should informed consent be structured so patients understand that blood tests are fallback options, not equivalent substitutes? What electronic health record (EHR) safeguards should prevent them from becoming first-line orders? The guideline offers little direction.

And in the absence of a framework, convenience tends to win. That is predictable. A blood draw feels easier than a stool test and far easier than colonoscopy. Clinicians under time pressure may offer it early. Health systems seeking higher screening uptake may integrate it into routine workflows. Patients may choose it because it sounds modern, simple, and less unpleasant. Administrators and payers may see it as scalable.

But if blood-based testing begins to substitute for more effective screening rather than rescue those who would otherwise remain unscreened, then its inclusion may ultimately weaken screening outcomes rather than improve them. That is the central concern. The issue is not whether blood-based testing should ever be used. It may have a role. The issue is that adding it to guidelines without operational guardrails makes misuse likely.

What would responsible implementation look like?

First, health systems could adopt a sequential offering framework. Under this model, blood-based screening should not sit in the same order set as stool test or colonoscopy. Average-risk patients should initially be offered only preferred screening options. Blood-based testing would enter the conversation only after the patient declines preferred options or fails to complete them after a defined outreach process.

Second, systems could require a documented informed-declination process before a blood test is ordered. Clinicians should document that the patient was offered preferred screening, informed that blood-based testing is less effective at detecting advanced precancerous lesions, and told that a positive result still requires diagnostic colonoscopy. This should not be left to variable clinician phrasing. It should be embedded in standardized scripts, decision aids, and EHR templates. If a guideline truly intends a test to be secondary, the ordering infrastructure should reflect that.

Third, institutions could build electronic ordering restrictions that reinforce the non-preferred status of these tests and only allow certain clinician or care team champions to enter orders for blood test.

Finally, any program using blood-based screening should include closed-loop colonoscopy follow-up tracking. A positive blood test without timely colonoscopy is not meaningful screening. Systems should measure positive test follow-up rates, time to diagnostic colonoscopy, and completion within a defined interval (e.g. 6 months). If these downstream processes are weak, then expanding blood-based screening may create false reassurance rather than cancer prevention.

These kinds of frameworks are not merely academic exercises; they are what determine whether a non-preferred test remains truly non-preferred in the real world. Guidelines shape care far beyond the exam room. They influence news coverage, payer decisions, quality measures, order sets, outreach campaigns, and patient perception. That is why language alone is not enough.

In the current environment, where novel blood tests receive outsized attention and enthusiasm, merely labeling them "non-preferred" will not reliably constrain their use. For many audiences, inclusion itself will read as validation. If blood-based colorectal cancer screening is to be included in recommendations at all, it should be accompanied by explicit guardrails. Otherwise, a guideline intended to preserve high-quality screening may instead create the impression that easier but less effective screening is good enough. And for colorectal cancer prevention, "good enough" is not a standard we should be normalizing.

Aasma Shaukat, MD, MPH, is practicing gastroenterologist and researcher in colon cancer screening, and a member of the MedPage Today editorial board.

Disclosures

Shaukat disclosed a consulting relationship with Iterative Health, Freenome Inc, UniversalDx, and Motus GI.

https://www.medpagetoday.com/opinion/second-opinions/121946