The third FDA-cleared Alzheimer's blood biomarker test is C2N Diagnostics' PrecivityAD2, cleared Aug. 20, 2026 to aid Alzheimer's diagnosis. For memory clinic patients, the safeguard is simple: use it only during evaluation for cognitive symptoms, not as screening or solo proof.
A blood biomarker test measures Alzheimer's-related proteins in blood to help doctors assess likely amyloid pathology. The Alzheimer's Association reports the Aug. 20 clearance in its clearance announcement. That timing matters because eligibility and result limits decide whether the headline applies to you.
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 guidance from Roche — Use this primary source to verify the official guidance.
- Read the official guidance from Alz — Use this primary source to verify the official guidance.
Table of Contents
- Who qualifies for PrecivityAD2?
- What does the blood draw measure?
- How accurate is it, and where does it wobble?
- How should memory clinic patients act on a result?
Who qualifies for PrecivityAD2?
PrecivityAD2 is cleared only for adults age 40 and older with signs or symptoms of cognitive impairment. NeurologyLive describes it as the first cleared test to extend below age 55 in its clearance report. A younger cutoff does not make it a checkup test for worried adults without symptoms. It fits patients already being evaluated for memory or thinking changes. It does not fit screening, family-risk testing without symptoms, or home decision-making.
If no clinician has documented cognitive signs, this clearance does not cover you. A fourth option soon followed. Roche reports FDA clearance of Roche/Eli Lilly Elecsys pTau217 on Aug. 24, 2026 for adults 55 and older. Do not mix the two headlines when you compare age rules and clinic claims.
What does the blood draw measure?
PrecivityAD2 uses high-resolution mass spectrometry on plasma. NeurologyLive reports it measures amyloid-beta 42/40 ratio plus percent p-tau217/np-tau217. Those values combine into an Amyloid Probability Score 2. Think of the amyloid ratio as a signal of plaque-related change.
Think of the p-tau217 measure as a signal of Alzheimer's-related tau change. The score weighs them together rather than asking one marker to decide alone. The practical gain is access. AJMC reports the benefit as a single blood-draw alternative to lumbar puncture or PET. That simpler step can speed diagnosis, care planning, and trial referral when treatments work best early.
How accurate is it, and where does it wobble?
In a 1,142-person symptomatic validation cohort versus amyloid PET or spinal fluid testing, NeurologyLive reports 97.6% positive predictive value and 93.1% negative predictive value. Those figures apply to clear positive or negative categories in symptomatic patients, not to everyone who wants testing. The middle category is the overreading trap. About 17.3% of validation patients received an intermediate "likely positive" result, with only 77.3% positive predictive value, NeurologyLive reports.
An intermediate result is a prompt for cautious follow-up, not a firm diagnosis. So read the result as three paths, not two. A clear negative lowers likelihood but still needs clinical judgment. A clear positive supports Alzheimer's pathology but still needs the full clinical picture. An intermediate result means pause and ask about next testing.
How should memory clinic patients act on a result?
Treat the test as one piece of a workup. AJMC reports it must be used alongside history, exam, cognitive testing, and sometimes imaging or spinal fluid testing in its clinic-use report. No score alone establishes Alzheimer's disease.
Bring details that help the clinician interpret the score: Ask what category your score falls in and what happens next for that category. For an intermediate or unexpected result, ask whether PET or spinal fluid testing is advised. Leave with a written plan for diagnosis, safety, support, and follow-up date.
- onset, examples, and timeline of memory or thinking changes
- medicines, sleep, mood, hearing, and medical conditions that affect cognition
- prior cognitive scores, scans, or spinal fluid results, if any
- your question about trial referral, care planning, or added testing
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