Test ID: PTAU217 P

pTau217, Plasma

Test Overview

Clinical Utility

Alzheimer’s disease (AD) is a neurodegenerative disorder hallmarked by extracellular amyloid plaques and intraneuronal neurofibrillary tangles of phosphorylated Tau (p-Tau) in the brain. The tau protein normally maintains microtubules assembly and stability of neuronal axons; however, tau protein with excessive phosphorylation can have pathological consequences. In patients with AD, aggregates of p-Tau can be detected by postmortem neuropathology evaluation or pre-mortem positron tomography (PET) imaging with specific tracers. Soluble p-Tau also accumulates in the CSF and can be detected in lumbar puncture samples, and ultra-sensitive methods including the technique used here can accurately detect p-Tau levels in the blood, which correlate well with CSF levels and with brain amyloid plaque burden. Plasma pTau217 levels correlate with amyloid-PET imaging and are more sensitive and specific than pTau181 in distinguishing AD from other neurodegenerative disorders.

Method

Single-molecule array (SiMoA)

Analytical Platform

Quanterix HD

Method Description

This test is a single molecule assay (Simoa) using an antibody to pTau217 developed by ALZpath Inc. This test was developed, and its performance characteristics determined by BCNI. It has not been accredited by DAP and has not been approved or cleared by Health Canada or the US FDA. The test was performed in a DAP, CAP and CLIA certified laboratory and is intended for clinical purposes.

Specimen

Specimen Type

Plasma

Containers

Collection Containers

Lavender top (EDTA)

Volume

Sample Volume

2.0 mL

Minimum Volume

0.5 mL

Patient Preparation

This test is not suitable for patients who have had a blood transfusion within 2-4 weeks, or who have had an allogenic bone marrow transplant.

Collection & Handling

Handling Information

Separate within 4 hours. Store and send frozen.

Additional Information

References:
Ashton et al., 2024. Diagnostic Accuracy of a Plasma Phosphorylated Tau 217 Immunoassay for Alzheimer Disease Pathology. JAMA Neurology. https://doi.org/10.1001/jamaneurol.2023.5319 Revised Criteria for Diagnosis and Staging of Alzheimer’s Disease: Alzheimer’s Association Workgroup. NIA-AA. Draft body text as of October 9, 2023. Noble, W., Hanger, D. P., Miller, C. C. J. & Lovestone, S. The Importance of Tau Phosphorylation for Neurodegenerative Diseases. Front. Neurol. 4, 83 (2013). Telser, J., Risch, L., Saely, C. H., Grossmann, K. & Werner, P. P-tau217 in Alzheimer’s disease. Clin. Chim. Acta 531, 100–111 (2022). Berry, K. et al. Hepatic and renal function impact concentrations of plasma biomarkers of neuropathology. Alzheimers Dement. Diagn. Assess. Dis. Monit. 14, e12321 (2022). Mielke, M. M. et al. Performance of plasma phosphorylated tau 181 and 217 in the community. Nat. Med. 28, 1398–1405 (2022). Gouda, M., Antwi-Berko, D., van Leeuwenstijn, M.S.S.A., Hussainali, Z., Bongers, B., Vanbrabant, J., in ’t Veld, S.G.J.G., Edelmayer, R.M., Stoops, E., Jeromin, A., Teunissen, C.E., Verberk, I.M.W., 2023. Plasma phosphorylated tau 217 levels are highly stable under common pre-analytical sample handling procedures. Alzheimer’s & Dementia 19, e078393. https://doi.org/10.1002/alz.078393

Stability

Ambient	Refrigerated	Frozen
3 days	7 days	28 days

240 days @ -80C

Rejection Criteria

Criteria	Specification
Hemolysis	Gross
Lipemia	Gross

Performance & Interpretation

Turnaround Time

18 days

Results

Negative

ng/L

≤0.34
Intermediate

ng/L

0.35 - 0.63
Positive

ng/L

>0.63

Comment

A test result ≤0.34 ng/L is a negative result and is consistent with a negative amyloid positron tomography (PET) scan.

A negative result indicates a low likelihood that a patient's cognitive impairment is due to Alzheimer's disease (AD).

A test result between 0.35 ng/L and 0.63 ng/L is considered intermediate. An intermediate result does not establish a diagnosis of AD or other cognitive disorder and has increased uncertainty in regard to amyloid PET positivity.

A test result > 0.63 ng/L is positive and is consistent with a positive amylold PET scan and amyloid pathology of Alzheimer's type. High pTau217 plasma levels alone do not establish a diagnosis of AD. Results should be interpreted in the context of other clinical signs and symptoms of AD.

Referral Location

Canada

Interface & Setup

HL7 Interface Codes

Order Code	Result Name	Result Codes	Units
PTAU217 P	Plasma pTau217	65615	ng/L

Test Version

Last Updated

2025-08-07