PrecivityAD2 is a blood test that aids detection of amyloid-plaque pathology linked to Alzheimer's disease. It is cleared as an adjunct to a standard clinical workup, with strong lab accuracy established and routine primary-care follow-through still less certain. The test fits into an evaluation for memory or thinking symptoms, not a checkup without symptoms. For patients and families, the practical issue is fit: whether symptoms qualify, what a score means, and what testing comes next.
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 the test measures
- How accurate is it in primary care?
- Who qualifies under the clearance?
- What does a result change?
What the test measures
PrecivityAD2 uses high-resolution mass spectrometry to measure amyloid-beta 42/40 and tau-217 ratios in plasma. Those results enter a proprietary algorithm reported as the Amyloid Probability Score 2, from 0 to 100.
According to WashU Medicine, the method detects amyloid-plaque pathology with over 90% accuracy and offers a single blood draw as a less invasive option than amyloid PET or spinal tap (WashU Medicine report). A higher score signals higher likelihood of amyloid pathology. A lower score signals lower likelihood.
How accurate is it in primary care?
A 2024 prospective JAMA study followed 1,213 primary- and secondary-care patients with cognitive concerns. As reported in JAMA, APS2 was about 90-91% accurate versus amyloid PET, while unaided primary-care physicians were about 61-63% accurate without biomarker testing (JAMA study PDF). That gap matters because early symptoms overlap with other causes. Mood change, sleep loss, thyroid disease, vitamin deficiency, medication effects, and vascular injury can mimic dementia.
A biomarker result helps a clinician sort that list. The comparison was against amyloid PET, a direct marker of plaque. It does not mean the blood test alone diagnoses Alzheimer's dementia. Clinical history, exam, cognitive testing, and often brain imaging still shape the final judgment.
Who qualifies under the clearance?
According to C2N Diagnostics, FDA clearance on Aug. 20, 2026 covers adults aged 40 and older with signs or symptoms of cognitive impairment, the first cleared Alzheimer's blood test down to age 40 (C2N clearance notice). Use is for symptomatic patients being evaluated for cognitive impairment. Testing sits alongside clinical assessment by a clinician experienced in such evaluation.
The cleared use excludes screening without symptoms. It also excludes standalone diagnosis. A result cannot by itself label a person as having or not having Alzheimer's disease. Routine performance in ages 40-50, effects of other illnesses and drugs, and payment coverage remain less established than laboratory accuracy. Patients in their 40s should expect careful review of symptoms, family history, and other causes before testing.
What does a result change?
The Alzheimer's Association's 2025 specialty-care guideline says qualifying blood tests may triage suspected Alzheimer's, with negative results helping rule out amyloid pathology and positive results requiring CSF or PET confirmation (Association guideline summary). That triage role can reduce unneeded scans and spinal taps. It can also speed referral when pathology looks likely.
For primary care, the Association issued a 2026 decision-support tool on when and how to use blood biomarkers. A primary-care visit may still end with watchful waiting, treatment of another cause, or referral to neurology, geriatrics, or memory care. Bring items that make the visit more decisive: Ask what a positive or negative score would change before giving blood.
- examples of memory, language, judgment, or navigation change, with dates
- current drugs, supplements, alcohol use, sleep, mood, and recent illness
- prior labs, brain scans, and family history of dementia
- goals for testing, including work, driving, and care planning
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