PrecivityAD2 is an FDA-cleared blood test for Alzheimer-related amyloid buildup in adults age 40 and older with cognitive symptoms. In memory clinics, clear positive and negative results show high predictive accuracy, while intermediate results need more workup and younger-onset data remain limited. NeurologyLive reported the Aug.
20, 2026 clearance as the first for symptomatic patients as young as 40 and the third cleared Alzheimer blood test overall FDA clearance report. The test is an aid to specialist evaluation. It does not replace clinical assessment.
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.
Table of Contents
- What changed for patients in their 40s?
- How accurate is it in symptomatic patients?
- Why does the intermediate result matter?
- Who should be tested?
- What gaps remain for younger-onset care?
What changed for patients in their 40s?
PrecivityAD2 measures plasma Aβ42/40, a ratio of amyloid fragments, plus percent p-tau217, a phosphorylated tau marker. High-resolution mass spectrometry quantifies both markers. The results combine into an Amyloid Probability Score 2. The score is reported as negative, positive, or intermediate likely-positive.
Negative points away from brain amyloid. Positive points toward it. C2N had expanded laboratory use from age 60 and older to 50 and older in August 2025 after added validation, according to C2N Diagnostics. The 2026 FDA clearance extended use to age 40 and older with symptoms. That change matters most for younger-onset evaluation, where other causes are also common.
How accurate is it in symptomatic patients?
In C2N's 1,142-person symptomatic validation against amyloid PET or spinal-fluid testing, positive results had 97.6% positive predictive value and negative results had 93.1% negative predictive value, as reported by NeurologyLive in the same FDA clearance report. Predictive value means the chance a result matches the reference test. The figures apply to clear results in symptomatic patients. An independent validation in 192 memory-impaired participants found 91% accuracy, 90% sensitivity, and 92% specificity at the preset cutoff, according to ReachMD reporting on an npj Dementia study independent accuracy analysis.
That group was 70% mild cognitive impairment and 30% dementia. Mild cognitive impairment means measurable thinking changes without loss of daily function. A 2024 prospective JAMA study of 1,213 symptomatic primary- and secondary-care patients reported areas under the curve of 0.96-0.97, according to the National Library of Medicine archive. Area under the curve measures discrimination between amyloid-positive and amyloid-negative cases. Predictive values were around 88-91%, better than clinician evaluation without biomarkers.
Why does the intermediate result matter?
About 17.3% of patients in the main validation fell in the likely-positive intermediate group. In that group, positive predictive value was only 77.3%, according to NeurologyLive. That is much less certain than a clear positive. Memory clinics cannot treat that result as confirmed amyloid positivity.
A patient could have amyloid pathology or could need repeat blood testing, spinal-fluid testing, or amyloid PET. PET uses a tracer to image amyloid in the brain. For a younger patient facing work decisions or treatment eligibility, this pause is practical. Ask the clinic what confirmatory test it will use, how soon, and whether treatment decisions wait for it.
Who should be tested?
The Alzheimer's Association guideline limits blood-biomarker testing to specialists evaluating cognitive impairment, as stated in its 2025 clinical practice guideline. It endorses triage use only for tests with at least 90% sensitivity and 75% specificity. It does not support screening without symptoms.
Practical checks before testing include: PrecivityAD2 remains an adjunct to clinical assessment, not a standalone diagnosis or healthy-person screen, according to C2N Diagnostics. A positive score alone does not establish Alzheimer's dementia. A negative score alone does not explain symptoms.
- ongoing memory, language, or reasoning symptoms noticed by patient or family
- specialist evaluation to rule out medication, sleep, mood, or medical causes
- plan for how positive, negative, and intermediate scores change next steps
- counseling about work, driving, family, and treatment implications
What gaps remain for younger-onset care?
Younger-onset means symptoms often start during working and parenting years. Differential diagnosis is wider and includes frontotemporal disorders, mood disorders, sleep apnea, and other neurologic causes. Amyloid testing narrows one question but does not sort the full list. The published accuracy data focus on symptomatic adults and memory-clinic-type groups.
They do not prove equal performance in every 40- to 50-year-old subgroup, comorbidity, or disease stage. Clinics should pair scores with history, neurologic exam, cognitive testing, and MRI. Bring a symptom timeline, medication list, family history, and a collateral informant to the visit. Ask whether the lab report was negative, positive, or intermediate likely-positive, and get the follow-up plan in writing.
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