An Alzheimer’s blood test called PrecivityAD2 just received U.S. Food and Drug Administration clearance, giving doctors a simpler way to look for the biological signs of Alzheimer’s disease in adults already showing memory or thinking problems. The clearance, reported in early September 2026, adds a mass-spectrometry-based option to a fast-growing category of blood tests that can flag amyloid plaque buildup in the brain without a spinal tap or a PET scan.
For anyone who has watched a parent or partner struggle with memory loss, the idea of a routine blood draw replacing a lumbar puncture or an expensive brain scan is welcome news. This article explains what actually changed, how PrecivityAD2 differs from other Alzheimer’s blood tests already on the market, and what a result can and cannot tell a patient.
What the FDA just cleared
PrecivityAD2, made by C2N Diagnostics and built on research from Washington University School of Medicine in St. Louis, is intended for adults aged 40 and older who already have signs or symptoms of cognitive decline. It is not a screening test for healthy people with no symptoms, and it does not diagnose Alzheimer’s disease on its own. Instead, it supports a fuller clinical evaluation that includes a doctor’s assessment of memory, daily functioning, and other possible causes of confusion, such as thyroid problems, vitamin deficiencies, or medication side effects.
The test measures the ratio of amyloid beta proteins (Aβ42 and Aβ40) along with two forms of tau protein (p-tau217 and total tau) in a blood sample, using high-resolution mass spectrometry rather than the antibody-based immunoassay method used by some competing tests. In the clinical validation study supporting the clearance, which involved 1,142 adults with cognitive symptoms, the test’s positive predictive value reached 97.6% and its negative predictive value reached 93.1%, when compared against amyloid PET scans and cerebrospinal fluid testing.
How PrecivityAD2 compares with other Alzheimer’s blood tests
PrecivityAD2 is not the first Alzheimer’s blood test to reach the market. The FDA cleared Fujirebio’s Lumipulse G pTau217/β-Amyloid 1-42 Plasma Ratio in May 2025, and Roche and Eli Lilly’s Elecsys pTau217 test followed in August 2026. All three rely on the same underlying biology, changes in amyloid and tau proteins that build up years before symptoms become obvious, but they use different laboratory techniques and different reference cutoffs.
| 検査 | 方法 | Cleared | 年齢区分 |
|---|---|---|---|
| PrecivityAD2 (C2N Diagnostics) | Mass spectrometry | September 2026 | 40 and older |
| Lumipulse G pTau217/Aβ1-42 (Fujirebio) | イムノアッセイ | May 2025 | 55 and older |
| Elecsys pTau217 (Roche/Eli Lilly) | イムノアッセイ | August 2026 | 55 and older |
None of these tests replaces a full clinical work-up. A complete evaluation for Alzheimer’s disease still relies on cognitive testing, a detailed history, and ruling out other causes of memory loss, something clinicians also do when investigating broader dementia symptoms and causes.
Why this matters now
Confirming amyloid pathology used to mean a PET brain scan, which is expensive and involves radiation, or a lumbar puncture, an invasive procedure that samples cerebrospinal fluid. A blood test lowers the barrier considerably, which matters because newer Alzheimer’s drugs that target amyloid work best when started early. A faster, cheaper way to confirm biological changes could shorten the path between the first worrying symptoms and a specialist referral.
That said, predictive values depend heavily on how likely a patient is to have Alzheimer’s pathology in the first place. In someone with no cognitive symptoms, the same test would be far less informative, which is exactly why PrecivityAD2 is restricted to symptomatic patients undergoing a specialist evaluation rather than offered as a general screening tool.
受診のタイミング
Occasional forgetfulness is common and does not usually signal Alzheimer’s disease. Consider scheduling an evaluation when memory or thinking problems start interfering with daily tasks such as managing finances, keeping appointments, or following a familiar recipe, or when a family member notices a change in judgment or personality. A primary care doctor can order initial blood work, including a vitamin B12 check、そして thyroid function testing, since deficiencies and thyroid disorders can mimic cognitive decline and are treatable.
最新の科学的進歩
Independent research over the past three years supports the broader shift toward blood-based Alzheimer’s diagnosis. A 2024 cohort study in JAMA Neurology found that a plasma p-tau217 immunoassay identified abnormal amyloid and tau pathology with high accuracy, comparable to spinal fluid testing, and that using a three-range reference cut the need for confirmatory testing by roughly 80% [Ashton et al., 2024]. In plain terms: for most patients, a blood result alone was clear enough to skip a second, more invasive test.
In 2025, the Alzheimer’s Association issued its first clinical practice guideline on blood-based biomarkers, concluding that tests reaching at least 90% sensitivity and 75% specificity can be used to decide who needs further testing, and that the very best-performing tests can substitute for a PET scan or spinal fluid analysis entirely in specialist settings. The guideline also cautioned that not all commercially available tests meet that bar, so results should always be interpreted by a clinician experienced in memory disorders rather than read in isolation.
A large 2025 systematic review and meta-analysis in The Lancet Neurology pooled data from more than 29,000 people across 113 studies and found that plasma p-tau217, the biomarker family PrecivityAD2 also measures, was the best-performing blood marker for identifying Alzheimer’s pathology, with sensitivity and specificity both around 88%. The authors noted that real-world studies, outside the tightly controlled research cohorts, are still needed to confirm how well these tests perform in everyday clinical practice, a reasonable note of caution before treating any single blood test as a final answer.
用語集
| 用語 | 定義 |
|---|---|
| アミロイド斑 | Clumps of amyloid-beta protein that build up between brain cells and are a hallmark feature of Alzheimer’s disease. |
| p-tau217 | A specific form of the tau protein that rises in blood and spinal fluid when Alzheimer’s-related brain changes are present. |
| Mass spectrometry | A precise lab technique that identifies and measures tiny amounts of specific proteins in a sample. |
| Amyloid PET scan | A brain imaging test that uses a radioactive tracer to visualize amyloid plaques directly. |
| 陽性的中率 | The probability that someone with a positive test result truly has the condition being tested for. |
| Cerebrospinal fluid (CSF) testing | Analysis of fluid collected via a lumbar puncture to measure Alzheimer’s-related proteins. |
よくある質問
Is PrecivityAD2 available to everyone with memory concerns?
No. It is intended for adults aged 40 and older who already have signs or symptoms of cognitive decline and are being evaluated by a clinician. It is not meant to screen healthy people with no symptoms, and predictive values would be less reliable in that group.
Can this blood test diagnose Alzheimer’s disease by itself?
No. It helps confirm whether amyloid plaques are likely present, which supports a diagnosis, but a full evaluation also requires a clinical history, cognitive testing, and ruling out other conditions such as depression, sleep disorders, or vitamin deficiencies that can cause similar symptoms.
How is PrecivityAD2 different from earlier Alzheimer’s blood tests?
It uses mass spectrometry rather than the immunoassay method used by the Fujirebio and Roche/Eli Lilly tests. All three measure related amyloid and tau biomarkers, and current guidance treats them as broadly comparable in accuracy when properly validated.
Will insurance cover this test?
Coverage decisions vary by insurer and region. FDA clearance typically makes it easier for laboratories and health systems to seek reimbursement, but patients should confirm coverage with their insurance provider and ordering physician before testing.
What should I do if I’m worried about my memory?
Start with a conversation with your primary care doctor, who can review your symptoms, order basic blood work to rule out reversible causes, and refer you to a memory specialist if needed. Bring specific examples of memory or thinking changes, ideally from someone who knows you well.
参考文献
- U.S. Food and Drug Administration — FDA Clears First Blood Test Used in Diagnosing Alzheimer’s Disease, 2025 — fda.gov
- National Institute on Aging (NIH) — How Is Alzheimer’s Disease Diagnosed?, 2026 — nia.nih.gov
- MedlinePlus (NIH/NLM) — Alzheimer Disease, 2026 — medlineplus.gov
- N. Ashton et al. — Diagnostic Accuracy of a Plasma Phosphorylated Tau 217 Immunoassay for Alzheimer Disease Pathology, JAMA Neurology, 2024 — consensus.app
- S. Palmqvist et al. — Alzheimer’s Association Clinical Practice Guideline on the use of blood-based biomarkers, Alzheimer’s & Dementia, 2025 — consensus.app
- J. Therriault et al. — Blood phosphorylated tau for the diagnosis of Alzheimer’s disease: a systematic review and meta-analysis, The Lancet Neurology, 2025 — consensus.app
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