The FDA cleared PrecivityAD2 on August 20, 2026, as the first FDA-cleared Alzheimer's blood test for adults 40 and older with signs or symptoms of cognitive impairment, and that clearance changes how a positive, negative, or borderline result should be read for someone already diagnosed with mild cognitive impairment (MCI). The test does not diagnose Alzheimer's disease by itself — it estimates the odds that amyloid plaque is present in the brain, and that estimate carries different weight depending on which of three result categories a person lands in. PrecivityAD2, made by C2N Diagnostics, lowers the eligible age from the prior lab-only version's 50-and-older cutoff to 40, a change the Alzheimer's Association also flagged in describing it as the third FDA-cleared blood-based Alzheimer's biomarker test. For someone already told they have MCI — a stage of measurable cognitive decline that has not yet progressed to dementia — the test's purpose is narrower than many people expect: it checks for one biological marker behind one possible cause of that decline, not for Alzheimer's disease as a whole.
Medical information disclaimer: This article is for general educational purposes only and does not provide medical advice, diagnosis, or treatment. Always consult a physician or other qualified health professional about symptoms, medications, tests, or treatment decisions.
Official resources:
- Read the official notice from Precivityad — Use this primary source to verify the official announcement.
- Read the official guidance from Alz — Use this primary source to verify the official guidance.
Table of Contents
- What PrecivityAD2 Actually Measures
- How to Read the Score Itself
- What a Positive Result Means — and Doesn't Mean — for an MCI Diagnosis
- Can the Test Be Repeated to Double-Check a Result?
- Who Should Be Cautious About How the Result Applies to Them
- Frequently Asked Questions
What PrecivityAD2 Actually Measures
PrecivityAD2 draws blood and measures two things: the ratio of amyloid-beta 42 to amyloid-beta 40, and the percentage of tau protein phosphorylated at a site called threonine-217 (%p-tau217), according to the Mayo Clinic Labs test catalog. Both proteins are hallmarks of Alzheimer's pathology — amyloid forms plaques, and tau forms tangles — and tracking their levels in blood is a stand-in for what used to require a PET scan or spinal fluid sample. The lab combines both measurements into a single number, the Amyloid Probability Score 2 (APS2), which runs from 0 to 100 and reflects the statistical likelihood that amyloid plaques are present in the brain, per the same Mayo Clinic Labs catalog.
A higher score means a higher probability of amyloid pathology, not a confirmed diagnosis of any specific dementia. For a person with MCI, this distinction matters because MCI has more than one possible underlying cause — Alzheimer's pathology is common, but vascular disease, Lewy body disease, and other conditions can also produce the same clinical picture. PrecivityAD2 only speaks to the amyloid question.
How to Read the Score Itself
Under the reference ranges used for the test, an APS2 result of 0 to 47 is reported as negative for amyloid pathology, and 48 to 100 is reported as positive, according to Mayo Clinic Labs. C2N's own clearance data add a third category, "Likely Positive," which occurred in 17.3% of participants in the validation study. The three categories do not carry equal confidence.
An outright positive result carried a 97.6% positive predictive value in that study, meaning it was right about 98 times out of 100. A "Likely Positive" result carried only a 77.3% positive predictive value — right roughly three times out of four — a gap reported by Practical Neurology. A negative result is generally reliable but not airtight: the same validation study found a 93.1% negative predictive value, which means roughly 1 in 15 negative results still misses amyloid pathology that is actually present, per Practical Neurology. A person with MCI and a negative result should understand that a small chance of a false negative remains, particularly relevant if cognitive symptoms continue to worsen despite the negative finding.
- **Positive (APS2 48-100):** High confidence (97.6% PPV) that amyloid pathology is present.
- **Likely Positive:** Lower confidence (77.3% PPV); about 1 in 4 of these results will not reflect true amyloid pathology.
- **Negative (APS2 0-47):** High confidence overall (93.1% NPV), but roughly 1 in 15 negative results still misses real amyloid pathology.
What a Positive Result Means — and Doesn't Mean — for an MCI Diagnosis
A positive PrecivityAD2 result in someone with MCI supports the idea that Alzheimer's-related amyloid pathology underlies their cognitive decline, but it does not confirm it on its own, according to Mayo Clinic Labs. The test detects a biological marker associated with Alzheimer's disease; it does not diagnose Alzheimer's disease as a clinical syndrome, and false positives do occur. Lab guidance is explicit that the result must be read together with a clinical exam, cognitive testing, neuroimaging, and routine lab work — not in isolation, per the same Mayo Clinic Labs catalog.
A clinician weighing a positive blood test alongside a normal neurological exam and stable cognitive scores over time may reach a different conclusion than one weighing it alongside progressive memory loss and an abnormal exam. A positive result also triggers an automatic follow-up: a reflex APOE genotype test, which checks for the E2, E3, and E4 variants of the APOE gene. Clinicians use this genetic information to counsel patients on risk and management once amyloid pathology has been flagged, as noted in the Mayo Clinic Labs catalog. A person who tests positive on PrecivityAD2 should expect this second test to follow automatically, not as a separate request.
Can the Test Be Repeated to Double-Check a Result?
No. Lab guidance states there is insufficient evidence to support using PrecivityAD2 as a serial test — that is, repeating it over time to track whether biomarker levels are changing or to monitor a response to treatment, according to Mayo Clinic Labs. A second blood draw cannot be used to confirm or reverse an initial result tied to an MCI diagnosis.
This matters for anyone tempted to retest after a borderline or unexpected result. The test was validated as a single measurement against a single question — is amyloid pathology likely present right now — not as a trend line. Someone who wants a different kind of confirmation should expect their clinician to turn to neuroimaging or other established diagnostic tools rather than a repeat blood draw.
Who Should Be Cautious About How the Result Applies to Them
The cutoffs used to classify a result as negative, likely positive, or positive were derived from a validation population that was predominantly White, according to Mayo Clinic Labs. How well those same thresholds perform in other racial and ethnic groups has not yet been established.
This is a direct limitation for any MCI patient outside the population the test was validated on. It does not mean the result is meaningless, but it means the confidence levels described above — the 97.6% positive predictive value, the 93.1% negative predictive value — were measured in a specific group and may not transfer precisely to every patient. A clinician interpreting a result for a patient outside that studied population has reason to weigh the blood test more cautiously relative to imaging or other clinical findings.
Frequently Asked Questions
Does a positive PrecivityAD2 result mean a person with MCI has Alzheimer's disease?
No. It indicates amyloid pathology is likely present, which supports an Alzheimer's-related cause of MCI, but a clinician must combine it with a clinical exam, cognitive testing, and neuroimaging before reaching a diagnosis.
Is a "Likely Positive" result as reliable as an outright positive?
No. An outright positive carries a 97.6% positive predictive value, while "Likely Positive" — about 17.3% of results in the validation study — carries only a 77.3% positive predictive value.
Can someone retest with PrecivityAD2 if they're unsure about their first result?
No. Lab guidance states there isn't enough evidence to support repeat testing to track biomarker changes or confirm an initial result.
Does a negative result rule out Alzheimer's-related amyloid pathology?
Not completely. The negative predictive value is 93.1%, so roughly 1 in 15 negative results still misses real amyloid pathology.
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