Memory Digest

Blood Tests for Alzheimer's

How new blood biomarker tests detect Alzheimer's-related brain changes, who they are for, and what results do—and don't—mean.

Last reviewed: October 2026

For decades, confirming Alzheimer's-related brain changes meant a PET scan or a spinal fluid (CSF) test after a lumbar puncture. In 2025 and 2026, the U.S. Food and Drug Administration (FDA) cleared several blood tests that detect proteins linked to amyloid plaques and tau changes. These tests make biological information about Alzheimer's Disease far more accessible—but they are tools within a full evaluation, not stand-alone diagnoses.

What the tests measure

Alzheimer's disease involves abnormal amyloid-beta and tau proteins in the brain. Blood tests measure related fragments in plasma, such as:

• pTau217 (phosphorylated tau at position 217)
• pTau181
• Ratios of amyloid peptides (for example β-amyloid 1-42 related ratios)
• Combined scores such as those used in PrecivityAD2

High (or ratio-defined) results correlate with amyloid pathology seen on PET or CSF. Accuracy in research and clearance studies has been high—often in the ballpark of matching PET or CSF in the high 80s to mid–high 90s percent range depending on the test and population—but no test is perfect.

FDA-cleared options (as of 2026)

Cleared blood tests for use in people with cognitive symptoms include (among others):

• Lumipulse G pTau217/β-Amyloid 1-42 Plasma Ratio (Fujirebio)—first FDA-cleared Alzheimer's blood test (2025), generally for adults 55+ with symptoms
• Elecsys pTau181 (Roche)—cleared to help rule out Alzheimer's pathology in primary care settings
• PrecivityAD2 (C2N Diagnostics)—cleared for adults 40 and older with signs or symptoms of cognitive impairment
• Elecsys pTau217 (Roche)—cleared as a single-biomarker option to support rule-in and rule-out of amyloid pathology in symptomatic adults (typically 55+)

Availability, insurance coverage and which labs offer which test continue to evolve. Your clinician chooses based on age, symptoms, setting and guidelines.

Who should get one?

These tests are intended for people who already have signs or symptoms of cognitive decline—for example suspected Mild Cognitive Impairment (MCI) or dementia—as part of Getting a Diagnosis. They are not recommended as casual screening for healthy people with no concerns. Testing asymptomatic people can cause anxiety, false reassurance or unnecessary follow-up without clear benefit.

Blood biomarkers are especially useful when:

• You need biological confirmation before considering anti-amyloid treatment such as Lecanemab (Leqembi) or Donanemab (Kisunla)
• PET or lumbar puncture is hard to access, costly, or medically difficult
• The cause of symptoms is unclear and Alzheimer's is one possibility

What a result means

Positive / elevated results suggest amyloid pathology consistent with Alzheimer's disease as a contributor. They do not by themselves prove that Alzheimer's is the only cause of symptoms, predict exact timing of decline, or replace clinical judgment. Mixed disease (Alzheimer's plus vascular changes, for example) is common.

Negative / low results make Alzheimer's pathology less likely and push evaluation toward other causes—including Reversible Causes of Memory Problems, Vascular Dementia, Lewy Body Dementia, Frontotemporal Dementia, depression, sleep disorders or medications.

False positives and false negatives occur. Kidney disease, certain assays, and borderline values need careful interpretation. Guidelines from groups such as the Alzheimer's Association emphasize using blood biomarkers with history, exam, Cognitive Screening Tests (MMSE, MoCA), and often imaging.

How testing fits the workup

A typical path:

1. History and informant interview; 10 Early Warning Signs of Alzheimer's and Dementia review
2. Cognitive screening (see Cognitive Screening Tests (MMSE, MoCA))
3. Blood tests for common medical causes (B12, thyroid, and others)
4. Brain imaging when indicated
5. Alzheimer's biomarker testing (blood, CSF or PET) when it will change care

Knowing amyloid status can open doors to disease-modifying therapy eligibility, clinical research (see Joining a Clinical Trial), and clearer planning—even when treatment is not chosen.

Practical questions to ask your doctor

• Is a blood biomarker appropriate for my age and symptoms?
• Which test, and will insurance cover it?
• What happens if it is positive? Negative? Borderline?
• Do I still need PET, CSF or MRI?
• Could results affect eligibility for Lecanemab (Leqembi) or Donanemab (Kisunla)?

Bottom line

Blood tests for Alzheimer's are a major advance: less invasive than spinal taps, more accessible than PET, and increasingly accurate for detecting amyloid-related pathology in people who already have cognitive symptoms. They support—never replace—a careful clinical diagnosis. If memory or thinking has changed, ask a clinician experienced in cognitive disorders whether a blood biomarker test belongs in your evaluation.

Sources

1. FDA: FDA Clears First Blood Test Used in Diagnosing Alzheimer's Disease
2. Alzheimer's Association: FDA Clears PrecivityAD2 Blood Test for Alzheimer's
3. Alzheimer's Association: FDA Clears Elecsys pTau217 Blood Test for Alzheimer's
4. National Institute on Aging: How Is Alzheimer's Disease Diagnosed?

Not medical advice. This article is general information, not a diagnosis or treatment plan for any individual. Talk with a doctor about your situation.

Related articles

• Getting a Diagnosis
• Alzheimer's Disease
• Mild Cognitive Impairment (MCI)
• Lecanemab (Leqembi)
• Donanemab (Kisunla)