The title's "third" premise is already outdated: a blood biomarker test measures disease-associated signals in blood, and the FDA now lists four cleared Alzheimer's blood tests. The closest third event was the August 20, 2026, clearance of C2N Diagnostics' PrecivityAD2 for symptomatic adults age 40 and older. For adults with new memory symptoms, the main point is unchanged: this test can support an evaluation, but it cannot diagnose Alzheimer's by itself. Start with a clinician-led cognitive evaluation, not a standalone blood result.
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:
- Explore the official data from FDA — Use this primary source to review the underlying data.
- Explore the official data from FDA — Use this primary source to review the underlying data.
Table of Contents
- Why "third" is already out of date
- What PrecivityAD2 actually measures
- Who falls within the cleared uses
- How much can you trust a result?
- What to do if memory changes are new
Why "third" is already out of date
Through August 24, 2026, the FDA's device database lists four cleared tests: one from Fujirebio, one from C2N, and two from Roche. precivityad2 briefly held the third position before Roche's Elecsys pTau217 became the fourth four days later.
The Alzheimer's Association described PrecivityAD2 as the first cleared Alzheimer's blood test for symptomatic adults as young as 40. FDA records identify it as clearance K253240 within the classification for immunoassay blood tests that assess amyloid pathology.
What PrecivityAD2 actually measures
PrecivityAD2 measures ratios involving amyloid and tau, two proteins associated with Alzheimer's disease. An algorithm combines those measurements into a score estimating the likelihood of Alzheimer's-associated amyloid pathology. That score is evidence about a biological feature, not a diagnosis of Alzheimer's disease or dementia.
It must be interpreted alongside the person's symptoms and clinical evaluation. C2N also said its FDA-cleared version was expected later in 2026. Its existing CLIA-validated laboratory offering remained available in the meantime, so patients should ask which version a clinician intends to order.
Who falls within the cleared uses
The tests do not all have the same intended population. The important distinctions are: Roche's test reports positive, intermediate, or negative categories for amyloid pathology, according to the company's August 24 announcement. These indications should not be treated as endorsements of testing people without symptoms.
- PrecivityAD2: adults 40 or older with symptoms of cognitive impairment.
- Fujirebio's Lumipulse ratio test: symptomatic adults 55 or older.
- Roche's Elecsys pTau217: people 55 or older with symptoms or complaints of cognitive decline.
How much can you trust a result?
No blood biomarker result is infallible. When the FDA cleared Fujirebio's test in May 2025, it specifically warned about false-positive and false-negative results. A false positive could create unnecessary alarm.
A false negative could provide reassurance even though memory symptoms still need investigation. An intermediate category may leave the clinical question unresolved. The Alzheimer's Association's clinical guideline says biomarker testing requires clinical context and warns that commercial tests vary in accuracy. It recommends clinician-led evaluation rather than treating a blood result as a diagnosis.
What to do if memory changes are new
Arrange a cognitive evaluation and bring concrete examples of what has changed, when it began, and how it affects daily life. Ask whether a cleared blood test fits your age and symptoms and how its result would influence the evaluation. Before agreeing to testing, ask:.
- What is the exact test name and version?
- Does its FDA-cleared use match my age and symptoms?
- What do positive, negative, or intermediate results mean for me?
- What would the clinician recommend after each possible result?
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