Alzheimer's Diagnosis Is Moving to a Blood Draw: What PrecivityAD2 Can Actually Tell You

A blood draw is becoming capable of answering a question that once often required a brain scan or spinal tap: does this person have the amyloid pathology associated with Alzheimer's disease? The FDA has now cleared C2N Diagnostics' PrecivityAD2 test for symptomatic adults aged 40 and older undergoing evaluation for cognitive decline. In its clearance-supporting validation cohort, clear positive and negative results were highly predictive when compared with amyloid PET or cerebrospinal-fluid testing.

That does not make PrecivityAD2 a simple yes-or-no Alzheimer's test for everyone. But it is another major step toward making biological confirmation of Alzheimer's pathology much easier to obtain.

What does the PrecivityAD2 Alzheimer's blood test detect?

Alzheimer's diagnosis has traditionally depended on a combination of symptoms, cognitive testing and, when biological confirmation is needed, evidence that characteristic pathology is present in the brain.

PrecivityAD2 focuses on amyloid pathology. It measures two blood-biomarker ratios using high-resolution mass spectrometry: amyloid beta 42/40 and phosphorylated tau217 relative to non-phosphorylated tau217. Those measurements are combined into an algorithmic result called the Amyloid Probability Score 2, or APS2.

The aim is not simply to detect whether somebody is forgetful. It is to estimate whether the brain contains the amyloid pathology strongly associated with Alzheimer's disease.

That distinction matters. Cognitive impairment can result from many causes, including vascular disease, medication effects, sleep disorders, depression and other neurodegenerative diseases. Amyloid pathology provides powerful biological evidence for Alzheimer's, but a blood result still has to be interpreted alongside the person's symptoms and clinical assessment.

The FDA therefore classifies the test as an aid to evaluation, not as a stand-alone diagnosis or general screening test.

How accurate is the Alzheimer's blood test?

The numbers behind the clearance are strong.

According to C2N's clearance announcement, the clinical validation study included 1,142 adults presenting with signs or symptoms of cognitive decline. Results were compared with established reference methods using amyloid PET imaging or cerebrospinal-fluid biomarkers.

Using its dual-cutoff approach, a clear Positive result had a 97.6% positive predictive value. In other words, within the studied symptomatic population, 97.6% of people classified as Positive had amyloid pathology according to the reference testing.

A Negative result had a 93.1% negative predictive value, meaning that a negative result was also strongly associated with absence of amyloid pathology.

There is an important middle category. A Likely Positive result occurred in 17.3% of participants and had a lower positive predictive value of 77.3%. Those patients may require additional clinical interpretation or confirmatory testing rather than treating the blood result as definitive.

Published data support the broader accuracy signal. An independent-cohort validation in 192 cognitively impaired participants reported 91% overall accuracy against amyloid PET, with 90% sensitivity and 92% specificity.

Predictive values are influenced by how common amyloid pathology is in the population being tested, which is another reason these figures should not be extrapolated to healthy people taking the test out of curiosity.

Could a blood test replace PET scans and spinal taps?

Potentially for some parts of the diagnostic pathway, and this is where blood biomarkers could have their largest impact.

Amyloid PET can visualize amyloid deposition in the brain, but it requires specialized scanning facilities and is relatively resource intensive. Cerebrospinal-fluid testing can provide excellent biomarker information but requires a lumbar puncture.

A blood sample is fundamentally easier to obtain, repeat and scale.

The FDA made the same point when it cleared the first blood-based Alzheimer's diagnostic device in 2025, noting that blood testing could reduce reliance on PET scans. PrecivityAD2 now extends regulated blood-based amyloid assessment to symptomatic adults as young as 40.

The likely future workflow is not necessarily blood replacing every other test. It may instead become a powerful first biological step: use a validated blood test to identify people with a very high or very low probability of amyloid pathology, then reserve PET or cerebrospinal-fluid testing for ambiguous cases or situations where further confirmation is needed.

That could mean fewer invasive procedures, fewer expensive scans and a shorter path from worrying symptoms to a biologically informed diagnosis.

Why does confirming amyloid matter more now?

A decade ago, identifying amyloid pathology often changed the diagnostic label more than the treatment options. That is no longer entirely true.

Anti-amyloid medicines such as lecanemab and donanemab are now used in early symptomatic Alzheimer's disease. Current LEQEMBI prescribing information instructs clinicians to confirm amyloid beta pathology before treatment begins.

That makes the diagnostic bottleneck more consequential. If a treatment targets amyloid, clinicians need convincing evidence that amyloid pathology is actually present.

A scalable blood test could therefore do more than make diagnosis convenient. It could help determine who should continue through an Alzheimer's treatment workup, who may need another explanation for cognitive decline and who should undergo additional confirmatory testing.

This does not mean that a positive blood test automatically qualifies someone for treatment. Disease stage, overall health, MRI findings, treatment risks and other factors still matter.

Can healthy people take PrecivityAD2 as an Alzheimer's screening test?

Not under the FDA-cleared intended use.

PrecivityAD2 is cleared for adults aged 40 and older who already have signs or symptoms of cognitive impairment and are being evaluated for Alzheimer's disease or another cause of cognitive decline. It is specifically not intended as population screening for asymptomatic people.

That boundary is important because Alzheimer's-associated biomarkers can begin changing before dementia becomes apparent, and interpreting a positive biomarker in someone with no symptoms raises a different set of scientific and clinical questions.

There is also a practical distinction between FDA clearance and immediate availability of the newly cleared device version. C2N says the FDA-cleared PrecivityAD2 version is expected to become available later in 2026. A laboratory-developed PrecivityAD2 test offered through the company's CLIA-certified laboratory is already available under its existing clinical pathway.

The larger transition, however, is already visible. Alzheimer's evaluation is moving away from a world in which biological confirmation routinely requires specialized imaging or spinal fluid and toward one in which a tube of blood can carry much of the same diagnostic information.

For patients facing unexplained memory or cognitive problems, that is not merely a more convenient laboratory test. It could substantially change how quickly and easily Alzheimer's pathology can be identified.

Scientific References & Further Reading

• FDA Clearance: “510(k) Premarket Notification K253240: PrecivityAD2 Test.” (U.S. Food and Drug Administration. PrecivityAD2 Test, K253240. Decision date August 19, 2026.)
• Clearance Validation: “FDA Clears C2N Diagnostics' PrecivityAD2 - First Alzheimer's Blood Test for Adults with Cognitive Symptoms as Young as 40.” (C2N Diagnostics. Published August 20, 2026.)
• Independent Validation: “Independent validation of the PrecivityAD2 blood test to identify presence or absence of brain amyloid pathology in individuals with cognitive impairment.” (Coppinger J, West T, Kirmess KM, et al. npj Dementia. 2025;1:23. doi:10.1038/s44400-025-00026-y.)
• Clinical Validation: “Clinical validation of the PrecivityAD2 blood test.” (Meyer MR, Kirmess KM, Eastwood S, et al. Alzheimer's & Dementia. 2024;20(5):3179-3192. doi:10.1002/alz.13764.)
• Diagnostic Context: “FDA Clears First Blood Test Used in Diagnosing Alzheimer's Disease.” (U.S. Food and Drug Administration. May 16, 2025.)

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Disclaimer: This article is for informational purposes only and does not constitute medical advice. It is not a substitute for diagnosis, treatment, or individualized medical care.