Alzheimer's Blood Test (p-tau217): Who It's For and What Results Mean

The p-tau217 blood test checks for the amyloid buildup behind Alzheimer's disease in people with memory or thinking changes. Here is who it is for, what a result means, how it differs from APOE genotyping, and how to get tested.

Published

October 5, 2026

Read time

10 min read

Medically reviewed by

Rhonda Collins, FNP-C

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An Alzheimer’s blood test measures proteins in your blood that change when amyloid plaques, the hallmark brain change of Alzheimer’s disease, build up. The most widely used single marker is phosphorylated tau 217 (p-tau217). These tests are meant for adults who already have memory or thinking problems and are being evaluated for the cause. They are not screening tests for people without symptoms. A raised result supports the presence of amyloid pathology but does not diagnose Alzheimer’s disease on its own, and a normal result does not explain why your symptoms started.

This guide covers what p-tau217 measures, which tests the FDA has cleared, who should and should not be tested, how to read each kind of result, how p-tau217 differs from an APOE gene test, and what ordering the test and following up on it look like.

What does the p-tau217 blood test measure?

The p-tau217 test measures one form of the tau protein, phosphorylated at position 217, in blood plasma. Labcorp describes it as a marker that “has been shown in the literature to be a surrogate of amyloid pathology” and uses it “to aid in the biological identification of Alzheimer’s disease” (Labcorp test 484390).

In plain terms, p-tau217 is an indirect look at whether amyloid plaques are present in the brain. Before blood tests, confirming amyloid meant an amyloid PET scan or a lumbar puncture to test cerebrospinal fluid (CSF). The Alzheimer’s Association’s 2025 clinical practice guideline compares blood tests against exactly those references: CSF biomarkers, amyloid PET or neuropathology (Palmqvist et al., Alzheimer’s & Dementia, 2025).

p-tau217 does not measure memory. It answers one narrower question: is Alzheimer’s-type amyloid pathology likely to be present right now?

Which Alzheimer’s blood tests are FDA-cleared?

As of October 2026, the FDA has cleared four blood tests in its category for amyloid pathology assessment (product code SET), according to the FDA’s 510(k) records:

The federal regulation for this device type, 21 CFR 866.5840, defines it as a test for “a patient presenting with cognitive impairment and being evaluated for AD and other causes of cognitive decline,” used “in conjunction with clinical assessment to increase diagnostic certainty” (eCFR, 21 CFR 866.5840). The individual clearances follow the same pattern:

• Fujirebio’s Lumipulse ratio test is for “adult patients aged 50 years and older presenting at a specialized care setting with signs and symptoms of cognitive decline” (Fujirebio, May 16, 2025).
• Roche’s Elecsys pTau217 test is for “individuals 55 years and older with signs, symptoms or complaints of cognitive decline” in primary and specialty care, and “is not intended to be used as a stand-alone test” (Roche, August 24, 2026).

The p-tau217 test available through Mito is a different test. It is Labcorp test 484390, which measures p-tau217 alone on Fujirebio’s Lumipulse platform. It is a laboratory-developed test, and Labcorp states: “This test was developed and its performance characteristics determined by Labcorp. It has not been cleared or approved by the Food and Drug Administration” (Labcorp test 484390). Labcorp says its cutoff “was established using samples from a well-established patient cohort characterized with amyloid PET data.” It is still worth knowing which test you are getting, because results from different methods “cannot be used interchangeably,” in Labcorp’s words.

Who should get an Alzheimer’s blood test?

The p-tau217 test is for adults with objective memory or thinking problems, such as mild cognitive impairment (MCI) or dementia, who are being evaluated for the cause and in whom Alzheimer’s disease is a possibility. That matches both the FDA device definition above and the Alzheimer’s Association guideline, whose scope is “individuals with objective cognitive impairment, including those with mild cognitive impairment (MCI) or dementia, who are undergoing evaluation by providers trained and experienced in memory disorders, where AD is the suspected underlying etiology” (Palmqvist et al., 2025).

Typical reasons someone in that group is tested include:

• memory loss, word-finding trouble or other cognitive changes that are getting worse and are being worked up for a cause;
• sorting out whether symptoms reflect Alzheimer’s pathology or something else;
• a specialist deciding whether further amyloid testing is needed.

Who should not get an Alzheimer’s blood test?

People without memory or thinking symptoms should not use p-tau217 as a screening test, even with a family history of Alzheimer’s disease. The Alzheimer’s Association guideline says plainly: “This guideline does not extend to cognitively unimpaired individuals, given the current lack of clinical relevance for BBM [blood-based biomarker] use in this population” (full text, PMC12306682). Every FDA clearance listed above is limited to people with signs or symptoms of cognitive decline.

There is also a statistical reason. How much a positive result means depends on how likely amyloid pathology was before the test. The guideline’s own example: a test with 90% sensitivity and 90% specificity has a positive predictive value of 69% when the pretest probability is 20%, rising to 97% when it is 80% (Palmqvist et al., 2025). The lower your starting likelihood, the more often a positive result is a false alarm.

If you have no symptoms but want to understand an inherited risk, that is a different question, and it is answered by a gene test rather than a pathology test. See the APOE section below.

What do p-tau217 results mean?

Labcorp reports p-tau217 as a single number in pg/mL with a reference range of 0.00 to 0.18 pg/mL. Labcorp states that “a pTau-217 value of >0.18 is a reported surrogate marker for beta amyloid pathology” (Labcorp test 484390).

Elevated result (above 0.18 pg/mL)

An elevated result means amyloid pathology is more likely. It does not, by itself:

• diagnose Alzheimer’s disease; or
• prove that Alzheimer’s pathology is causing your symptoms.

The Alzheimer’s Association guideline describes a “triaging test” as one where “a negative result rules out AD pathology with high probability, whereas a positive result should be confirmed using another method, such as CSF AD biomarkers or amyloid PET.” It also cautions that “many commercially available BBM tests do not meet these thresholds, especially using a single cutoff,” and that the tests “do not serve as a substitute for comprehensive clinical evaluation” (Palmqvist et al., 2025). The usual next steps after an elevated result are a specialist evaluation and, when the answer would change care, confirmatory amyloid PET or CSF testing.

Normal result (0.18 pg/mL or below)

A result in the reference range makes amyloid pathology less likely. It does not mean your symptoms are imagined or unimportant. Memory loss has many causes that a p-tau217 test does not look at, including depression and other mental health conditions, alcohol and some medicines, low vitamin B1 or B12, stroke, and other types of dementia (MedlinePlus, memory loss). Our brain fog testing guide covers the blood tests that check several of those causes.

Intermediate or borderline result

Some FDA-cleared tests use two cutoffs and report three categories. Roche’s Elecsys pTau217 test “provides positive, intermediate and negative result categories” (Roche, 2026), and in Fujirebio’s clearance study 20% of patients fell in the uncertain middle zone and needed further testing (Fujirebio, 2025).

Labcorp’s p-tau217 report has one reference range, not an intermediate category, so it will not label a borderline value for you. The reason two-cutoff tests exist is that values near a single cutoff are less certain: in the studies the guideline reviewed, “values above the upper cutoff confirmed AD pathology with high certainty and values below the lower cutoff ruled out AD pathology with high certainty” (PMC12306682). A single-cutoff report cannot show how certain a value close to 0.18 pg/mL is.

p-tau217 vs APOE: disease biomarker vs risk gene

p-tau217 and APOE genotyping are often mentioned together, but they answer different questions.

APOE e4 is a risk gene, not a diagnosis. MedlinePlus Genetics, from the National Library of Medicine, puts it this way: “People who inherit one copy of the APOE e4 allele have an increased chance of developing the disease; those who inherit two copies of the allele are at even greater risk.” It adds: “Not all people with Alzheimer’s disease have the APOE e4 allele, and not all people who have this allele will develop the disease” (MedlinePlus Genetics, APOE gene).

So a person with no symptoms who carries APOE e4 has a higher risk, not Alzheimer’s disease. A person with symptoms and a raised p-tau217 has evidence of the underlying pathology, whatever their APOE result. Because an APOE result has personal and family implications, genetic counseling before or after testing is worth considering. You can read more about the APOE Alzheimer’s disease risk genotype test on its product page.

How to get an Alzheimer’s blood test

Getting the most out of a p-tau217 result depends on what happens around it, not only on the blood draw.

1. Start with the symptoms. A p-tau217 result is most useful as one part of an evaluation of memory and thinking, alongside a cognitive assessment and checks for other causes. If you have new or worsening memory problems, talk with your doctor about that evaluation.
2. Order the test. You can order the p-tau217 blood test through Mito. The sample is a blood draw at a lab near you. No fasting is needed. The plasma has to be collected in an EDTA tube, spun and frozen, which is why it is drawn at a lab visit. Results typically post in 5 to 7 days, and the test is HSA/FSA eligible. With a Mito membership, a clinician reviews your result.
3. Bring the result to the evaluation. Share the number and the lab name (Labcorp, test 484390) with the doctor or memory specialist evaluating your symptoms, because results from different test methods are not interchangeable.
4. Follow up on an elevated or borderline result. A raised value usually leads to a specialist visit and, when it would change care, amyloid PET or CSF testing to confirm it. Confirmation matters for treatment too: the Alzheimer’s Association guideline notes that the newer amyloid-targeting therapies “require biomarker confirmation of amyloid pathology to determine treatment eligibility” (PMC12306682). Labcorp also lists p-tau217 as usable “for monitoring patients on newly approved anti-amyloid therapy.”
5. Keep looking after a normal result. A normal p-tau217 makes Alzheimer’s pathology less likely, so the next step is the rest of the workup for other causes of your symptoms.

A blood result from any lab is not an Alzheimer’s diagnosis on its own. The diagnosis comes from a clinician who puts the biomarker together with your history, examination and cognitive testing.

Sources

• Labcorp. Test 484390: Phosphorylated Tau 217 (pTau-217), Plasma. Read October 5, 2026.
• Palmqvist S, Whitson HE, et al. Alzheimer’s Association Clinical Practice Guideline on the use of blood-based biomarkers in the diagnostic workup of suspected Alzheimer’s disease within specialized care settings. Alzheimer’s & Dementia. 2025;21(7):e70535. PMID 40729527.
• Pahlke S, et al. Blood-based biomarkers for detecting Alzheimer’s disease pathology in cognitively impaired individuals within specialized care settings: a systematic review and meta-analysis. Alzheimer’s & Dementia. 2025;21(11):e70828.
• U.S. Code of Federal Regulations. 21 CFR 866.5840, Alzheimer’s disease pathology assessment test.
• U.S. Food and Drug Administration. 510(k) records K242706, K252163, K253240 and K261686.
• Fujirebio. Fujirebio receives marketing clearance for Lumipulse G pTau 217/β-Amyloid 1-42 Plasma Ratio. May 16, 2025.
• Roche. Roche receives FDA clearance for Elecsys pTau217. August 24, 2026.
• MedlinePlus. Memory loss. National Library of Medicine.
• MedlinePlus Genetics. APOE gene. National Library of Medicine.