Science

An Alzheimer's blood test just got cleared — and the clearance says it is not for screening

Medically reviewed by Longevity Benchmark Editorial Last reviewed 2026-08-24

The FDA cleared C2N Diagnostics' PrecivityAD2 for adults 40+ with signs of cognitive impairment. The indication explicitly excludes screening.

August 24, 2026 · Science · Biomarkers · Blood testing

What happened

C2N Diagnostics announced on August 20, 2026 that the FDA cleared PrecivityAD2, a blood test for Alzheimer's-associated amyloid pathology, describing it as the first such cleared test available to patients as young as 40. The assay measures plasma beta-amyloid and tau peptide isoforms by high-resolution mass spectrometry — reported as the Aβ42/40 ratio and %p-tau217 — and combines them into an amyloid probability score, APS2, on a 0 to 100 scale. The underlying technology was invented at Washington University School of Medicine in St. Louis, whose announcement notes that C2N was founded by WashU researchers and that the university holds related patent applications. C2N says the cleared version is expected to be available later this year, with its existing CLIA laboratory version remaining available in the meantime.

The short version

The most important sentence in this announcement is a restriction, not a capability. C2N states the test is "not intended as a screening or stand-alone diagnostic test," and the cleared indication is limited to adults 40 and older who already have signs or symptoms of cognitive impairment and are being evaluated for them. That is the opposite of how blood biomarkers are usually sold on the consumer longevity market, where the pitch is breadth applied to people who feel fine. A regulator agreeing that a test performs well inside a symptomatic workup is not a regulator agreeing it should be added to an annual panel.

What it means for you

If you follow the platforms we benchmark, the reflex when a blood test clears the FDA is to ask when it lands on a panel. Here, the clearance itself answers that: the indication C2N publishes covers adults aged 40 years and older presenting with signs or symptoms of cognitive impairment while undergoing evaluation for Alzheimer's disease or other cognitive decline, used together with clinical assessment, by professionals experienced in evaluating cognitive impairment. Every clause in that sentence narrows it. The test is positioned as one input a specialist folds into a workup that is already underway — closer in spirit to a targeted follow-up than to a discovery panel.

The distinction between an aid to diagnosis and a screening test is the single most useful concept a reader of this site can take from this news, because it recurs constantly and is routinely blurred in marketing. A test earns strong numbers by being pointed at people with a meaningful chance of having the condition. Aim the same assay at people without symptoms and the arithmetic changes underneath it: positive and negative predictive values move with how common the condition is in the group tested, which is why C2N's figures are reported alongside the population they came from. The same logic sits behind our coverage of Galleri, a blood test aimed at a genuinely asymptomatic population, and it is why that product's evidence conversation looks so different from this one despite both being blood draws.

The number we would actually read first is not in the headline. Alongside a positive result carrying a 97.6% positive predictive value and a negative result carrying a 93.1% negative predictive value, C2N's release describes an intermediate "Likely Positive" band with a 77.3% positive predictive value that occurred in 17.3% of subjects. Roughly one in six people in that validation set received a result materially less decisive than either headline figure. Intermediate bands are the part of biomarker testing that determines what the experience is actually like — they are where the additional imaging, the repeat draw, and the waiting live. Any panel that reports a marker on a continuous scale has this property, whether or not it publishes the band.

There is a broader point about sequencing that applies well beyond this test. The blood-testing services we review across the platform hub compete largely on breadth of panel, and breadth is easy to market because more markers reads as more thorough. What this clearance illustrates is that the value of a marker is inseparable from who is being tested and what happens next. A result that would trigger a defined clinical pathway in a symptomatic 62-year-old may trigger nothing but anxiety in an asymptomatic 41-year-old, and no amount of analytical precision changes that. Our guide to normal versus optimal ranges covers the same trap from the other direction.

What this clearance does not establish

Clearance is a regulatory judgment about a specific intended use, not a general endorsement. The validation C2N describes involved 1,142 subjects who already had signs or symptoms of cognitive decline, benchmarked against amyloid PET visual read or cerebrospinal fluid testing — so it measures agreement with existing amyloid tests in symptomatic patients, not whether testing improves anyone's outcome, and not what the test would do in people without symptoms. Amyloid pathology is also not the same thing as dementia: the test is described as identifying amyloid pathology associated with Alzheimer's disease, to be interpreted alongside clinical history. Nothing here tells you whether you should be tested. That is a conversation with a clinician who evaluates cognitive impairment.

How this fits what we already know

We have written repeatedly about the gap between analytical performance and decision usefulness in consumer testing — most recently in our briefing on epigenetic clocks losing to conventional risk factors in a Finnish cohort, and in our look at how little the highest-evidence screening test gets discussed. This clearance is a useful counterweight to both, because it is an example of the system working in the direction we usually complain it does not: a test with strong performance data, cleared with an indication tight enough to say out loud what it is not for. When you evaluate the panels on our platform comparisons or read our notes on at-home blood test accuracy, the question this news should sharpen is not "how many markers" but "validated in whom, and what would a result change."

Sources

C2N Diagnostics, "FDA Clears C2N Diagnostics' PrecivityAD2® — First Alzheimer's Blood Test for Adults with Cognitive Symptoms as Young as 40," August 20, 2026, businesswire.com (accessed August 24, 2026). Source for the indication, intended-use limitation, analytes, APS2 score, validation size and all predictive values.
WashU Medicine, "FDA clears blood test to aid evaluation for Alzheimer's disease," medicine.washu.edu (accessed August 24, 2026). Source for the technology's origin and the university's disclosed relationship with C2N.
Medical Xpress, "FDA clears blood test to aid evaluation for Alzheimer's disease," August 24, 2026, medicalxpress.com (accessed August 24, 2026).

Frequently Asked Questions

Can I buy this test if I feel fine and just want to know my Alzheimer's risk?

That is not what the FDA cleared it for. C2N states the cleared indication covers adults aged 40 and older who present with signs or symptoms of cognitive impairment and are undergoing evaluation, and that the test is not intended as a screening or stand-alone diagnostic test. Screening means testing people without symptoms, which is a different question with different evidence behind it. Whether any testing is appropriate for you is a determination for a clinician experienced in evaluating cognitive impairment.

What do the 97.6% and 93.1% figures actually mean?

They are predictive values from C2N's clinical validation, which the company describes as 1,142 subjects with signs or symptoms of cognitive decline, compared against amyloid PET visual read or cerebrospinal fluid biomarker testing. C2N reports a 97.6% positive predictive value for ruling in and a 93.1% negative predictive value for ruling out. Predictive values are not fixed properties of a test — they depend on how common the condition is in the group being tested. These were measured in symptomatic patients under evaluation, so they describe that population and would not carry over unchanged to people without symptoms.

What is the "Likely Positive" result and why does it matter?

C2N's release describes a third, intermediate outcome alongside clearly positive and clearly negative results: a Likely Positive result carrying a 77.3% positive predictive value, which occurred in 17.3% of subjects. That is the part the headline accuracy numbers do not convey. Roughly one in six people in the validation set landed in a band substantially less certain than either endpoint, and an intermediate biomarker result generally means the clinical workup continues rather than concludes.

Is this the same thing as the Alzheimer's markers on a consumer longevity panel?

No. This is a specific plasma assay measuring the Aβ42/40 ratio and %p-tau217 by high-resolution mass spectrometry, combined into an amyloid probability score, and it is cleared for use inside a clinical evaluation of someone with cognitive symptoms. Broad consumer panels are sold to people without symptoms and are a different exercise entirely. If a consumer platform offers something it describes as an Alzheimer's or brain-health marker, the questions to ask are which analyte it measures, in whom it was validated, and what a result would change.

How much does it cost and where can I get it?

C2N's announcement states the FDA-cleared version is expected to be available later this year and that the existing CLIA laboratory version remains available. The release we read does not state a price for the cleared test, so we are not publishing one. Access runs through a healthcare professional evaluating cognitive symptoms, not through a direct consumer checkout.