p-tau217 (Phosphorylated Tau 217)
A form of tau protein in blood plasma. Higher levels are linked to amyloid build-up in the brain, and each lab's method has its own cutoffs.
AI-verified against cited sources. Awaiting expert reviewAlso called p-tau217, pTau217, P-tau217LOINC 104663-0
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What it is
Tau is a protein inside nerve cells. In Alzheimer's disease, tau picks up extra phosphate groups, and some of this phosphorylated tau reaches the blood. p-tau217 is tau with a phosphate group at position 217. Blood levels rise as amyloid builds up in the brain, which can begin before symptoms. Each lab uses its own method, with its own scale and cutoffs, so results from different labs cannot be compared directly.
Why it matters
For people with memory or thinking changes, p-tau217 is one of the most accurate blood markers of amyloid build-up, an early change in Alzheimer's disease. Specialists use it to decide whether more testing, such as an amyloid PET scan or a spinal fluid test, is needed. Some versions are cleared by the FDA for adults who already have symptoms. A result is a clue, not a diagnosis. These tests are not meant for screening people with no symptoms.
If it’s low
A low p-tau217 (a negative result) makes amyloid build-up in the brain less likely as the reason for memory or thinking changes. It does not rule out other causes, so other reasons for your symptoms should still be looked into. In the Roche study, about 5 of every 100 negative results still matched a positive amyloid PET scan.
Common causes
- No amyloid build-up in the brain
- Another cause of memory or thinking changes, such as depression, certain medicines or another kind of dementia
What can help
- Ask your clinician which other causes of your symptoms should be looked into
- Tell your clinician if your symptoms change or get worse
If it’s high
A high p-tau217 means there is more of this protein in your blood than usual. In people with memory or thinking changes, a high result is linked to amyloid build-up in the brain. It is not a diagnosis. Kidney disease can also raise the level, and some older adults with no symptoms have high results too.
Common causes
- Amyloid build-up in the brain linked to Alzheimer's disease
- Reduced kidney function, which can raise the level by itself
- Early Alzheimer-type changes in an older adult who has no symptoms yet: in the Roche reference study of 167 cognitively normal adults aged 55 to 80, about 9% were above the positive cutoff
- A result close to the lab's cutoff, where small measurement differences can change the category
What can help
- Talk with your clinician or a memory specialist about what the result means alongside your symptoms and exam
- Ask whether your kidney function (eGFR) has been checked, since kidney problems can raise p-tau217
- Ask whether an amyloid PET scan or spinal fluid test is worth considering to confirm the result
What can affect your result
- Method: each lab's assay has its own scale and cutoffs (for example Roche 0.223 and 0.378 pg/mL, Mayo 0.185 and 0.325 pg/mL, ARUP 0.13 and 0.20 U/mL)
- Kidney function: lower eGFR raises p-tau217 in studies, in people with and without amyloid
- Body mass index and anemia: levels vary with both
- Age: more cognitively normal older adults have results above the cutoff at older ages (Roche: about 5% of adults aged 55–70 versus about 20% of those aged 71–80 were above the upper cutoff)
- Sex: in the Roche reference group, the upper end of the usual spread was higher in men than in women
- How common amyloid is in the group tested, which changes how often a positive result is right
- Sample handling: plasma collection tube, spin time and freezing rules differ by lab
- In the FDA studies of the Roche assay, hemoglobin, bilirubin, lipids, biotin, rheumatoid factor, albumin, immunoglobulins and 43 common and special-use drugs did not interfere significantly.
- Reduced kidney function raises plasma p-tau217 on its own, in people with and without amyloid in the brain.
- Body mass index and anemia are also linked to shifts in p-tau217 levels.
- Handling rules differ by lab. ARUP asks for plasma to be separated within 2 hours and shipped frozen, while Mayo allows up to 72 hours at room temperature.
- Each lab method has its own scale and cutoffs, so results are not interchangeable between labs or kits.
Rises slowly over years in people with amyloid build-up: in one study, p-tau217 increased year over year only in amyloid-positive people. It is not a short-term tracking marker.
When to talk to a clinician
A blood p-tau217 result is not an emergency on its own. Talk with a clinician if you or your family notice memory or thinking changes that are new, getting worse or getting in the way of daily life. Call 911 or your local emergency number for sudden confusion, trouble speaking or face drooping.
Questions you could ask
- Is this test appropriate for me, given my symptoms and age?
- Which lab and method was used, and can it be compared with any earlier results?
- Was my result positive or in the intermediate zone, and which cutoffs did my lab use?
- Should we confirm it with an amyloid PET scan or a spinal fluid test?
- Could my kidney function be affecting this result?
- What other causes of my symptoms should we look into?
Questions people ask
Why do labs use different cutoffs for p-tau217?
Each lab uses its own assay with its own calibration. For example, Roche's FDA-cleared test uses 0.223 and 0.378 pg/mL, Mayo Clinic Laboratories uses 0.185 and 0.325 pg/mL, and ARUP reports in U/mL with cutoffs of 0.13 and 0.20. Numbers from different assays cannot be compared, so use your own lab's cutoffs.
What does an intermediate result mean?
It means the test cannot say either way. About 1 in 5 results land in this zone (19.9% in Roche's main study and 17% in ARUP's). In Roche's study, about 38 of every 100 people with an intermediate result had a positive amyloid PET scan. Clinicians often suggest further testing, such as an amyloid PET scan or spinal fluid test, or repeat testing if symptoms continue or change.
Does a positive result mean I have Alzheimer's disease?
No. ARUP's report says a positive result by itself does not establish a diagnosis of Alzheimer's disease or another cognitive disorder, and Roche's FDA-cleared test must be used together with other clinical information. In Roche's main study, about 1 in 9 positive results did not match a positive amyloid PET scan. Clinicians combine the result with symptoms, an exam and other tests.
Can I use p-tau217 to check my risk if I have no symptoms?
These tests were built and tested in people who already have memory or thinking changes. Mayo says its test should not be ordered for people with no cognitive symptoms or used to predict dementia, and the Alzheimer's Association guideline does not cover people without symptoms. A positive result in someone with no symptoms cannot tell whether, or when, memory problems will develop.
Does kidney disease change my p-tau217 result?
It can. In studies, people with reduced kidney function have higher p-tau217 even without amyloid in the brain. For an eGFR of 45 versus 60 in people without amyloid, levels were about 31% to 55% higher, depending on the assay. A ratio such as %p-tau217 is less affected. If you have kidney disease, tell the clinician who is reading your result.
Show the science and sources
For clinicians and researchers
p-tau217 is tau phosphorylated at threonine 217. Plasma levels rise about 250–600% in Alzheimer's dementia compared with other neurodegenerative diseases, and the largest relative rise is usually seen with p-tau217 (Hansson 2022). In BioFINDER-2, plasma p-tau217 separated Alzheimer's dementia from other neurodegenerative diseases with an AUC of 0.96 (Palmqvist 2020). In a head-to-head study, mass-spectrometry p-tau217 reached an AUC of 0.947 for amyloid status and the best p-tau217 immunoassays 0.886–0.889 (Janelidze 2023). Immunoassays are scaled differently. The Roche Elecsys Phospho-Tau (217P) Plasma assay (FDA K261686, cleared 2026-08-19, adults 55 or older with signs, symptoms or complaints of cognitive decline; measuring range 0.0560–2.40 pg/mL) uses 0.223 and 0.378 pg/mL: in 958 people with amyloid PET, 33.6% of results were positive (88.5% PET-positive), 19.9% intermediate (37.7%) and 46.5% negative (4.7%). Mayo's chemiluminescent enzyme immunoassay uses 0.185 and 0.325 pg/mL (adults 50 and older, not for cognitively unimpaired people), and ARUP's kit-based test reports 0.13 and 0.20 U/mL (adults 60 and older, 524 people, 90% sensitivity and specificity, 17% indeterminate). Chronic kidney disease raises p-tau217; for an eGFR of 45 versus 60 in amyloid-negative people, one study estimated +31% (ALZpath assay) and +55% (C2N p-tau217), and the %p-tau217 ratio was less affected (Bornhorst 2025). Kidney function, BMI and anemia shift the best cutoff, and a double-cutoff approach reduces false classifications at the cost of 12–39% intermediate results (Yun 2026). The 2025 Alzheimer's Association guideline applies to adults with objective cognitive impairment in specialized care and assessed single cutoffs only.
LOINC 104663-0 (primary). Specimen: plasma.
Sources
- Elecsys Phospho-Tau (217P) Plasma, 510(k) K261686 decision summary, U.S. Food and Drug Administration (2026)
- Phospho-Tau 217, Plasma (Mayo test ID PT217), Mayo Clinic Laboratories Extended Catalog (testcatalog.org) (2026)
- Phospho-Tau 217, Plasma (ARUP test 3019017), ARUP Laboratories (2025)
- Phospho-Tau 217, Plasma: Additional Technical Information (ARUP Consult), ARUP Laboratories (2025)
- Discriminative Accuracy of Plasma Phospho-tau217 for Alzheimer Disease vs Other Neurodegenerative Disorders, JAMA (2020)
- Head-to-head comparison of 10 plasma phospho-tau assays in prodromal Alzheimer's disease, Brain (2023)
- Diagnostic Accuracy of a Plasma Phosphorylated Tau 217 Immunoassay for Alzheimer Disease Pathology, JAMA Neurology (2024)
- Quantitative Assessment of the Effect of Chronic Kidney Disease on Plasma P-Tau217 Concentrations, Neurology (2025)
- Plasma Phosphorylated Tau 217 Cutoffs for Amyloid Pathology and Kidney Function, Body Mass Index, and Anemia, JAMA Neurology (2026)
- The Alzheimer's Association appropriate use recommendations for blood biomarkers in Alzheimer's disease, Alzheimer's & Dementia (2022)
- 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)
- LOINC 104663-0: Tau protein.phosphorylated 217 [Mass/volume] in Serum or Plasma by Immunoassay, LOINC via NLM Clinical Tables
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.