MSD S-PLEX · fg/mL Sensitivity

MSD p-Tau217 Ultrasensitive Assay Service

Quantify plasma phosphorylated Tau at threonine 217 at femtogram-per-milliliter sensitivity — a leading blood-based biomarker for Alzheimer's disease research, cohort enrichment, and longitudinal therapeutic monitoring studies.

Plasma p-Tau217 has emerged as a key biomarker in Alzheimer's disease research, demonstrating strong associations with cerebral amyloid and Tau pathology in multiple independent cohorts. Our MSD S-PLEX assay achieves the sensitivity required to reliably quantify this ultra-low-abundance analyte in plasma — supporting non-invasive research screening, cohort enrichment strategies, and longitudinal biomarker tracking in therapeutic development programs.

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p-Tau217 in Alzheimer's Disease Research

Phosphorylated Tau at threonine 217 (p-Tau217) is a soluble fragment of hyperphosphorylated Tau protein that can be detected in the bloodstream. In Alzheimer's disease research, p-Tau217 levels reflect cerebral amyloid and Tau pathology, showing strong concordance with PET imaging findings. This makes p-Tau217 one of the most intensively studied blood-based biomarkers for AD research applications.

 Research Findings on p-Tau217
Stronger signal than p-Tau181: Plasma p-Tau217 shows approximately 2–3× greater fold-change between Aβ-positive and Aβ-negative research participants compared to p-Tau181 in published cohort studies.
Correlates with Tau PET: Plasma p-Tau217 levels correlate with Tau PET SUVR in Braak-associated brain regions in multiple independent cohorts.
Early elevation: p-Tau217 elevations are detectable in cognitively unimpaired Aβ-positive individuals, supporting its use in preclinical AD research.
Disease specificity: Published studies report that p-Tau217 can differentiate AD pathology from other neurodegenerative conditions in research settings.
Clinical trial utility: p-Tau217 has been incorporated as a screening biomarker in multiple Alzheimer's therapeutic trials to enrich for Aβ-positive participants.

Research Applications

Cohort enrichment — identify research participants likely to have cerebral amyloid pathology using a blood draw, reducing need for PET screening in observational and interventional studies.
Longitudinal biomarker monitoring — track p-Tau217 trajectories over time to assess pharmacodynamic effects of anti-amyloid and anti-Tau investigational therapies.
Population-based research — scalable, cost-efficient blood biomarker for large epidemiological and aging cohort studies.
Prognostic research — investigate p-Tau217 as a predictor of cognitive trajectories in longitudinal observational cohorts.
Translational studies — support therapeutic development with a blood-based biomarker that reflects target engagement and disease modification.

p-Tau217 Assay Performance

Representative performance metrics from peer-reviewed studies using plasma p-Tau217 for Alzheimer's pathology research.

0.94 AUC

AD Pathology vs. Controls
(Representative published value)

2–3×

Fold Change vs. p-Tau181
In Aβ+ vs. Aβ− comparisons

~10 yr

Pre-Symptom Elevation
Longitudinal cohort data

Note: Values are illustrative and drawn from published literature for informational purposes. Individual study results vary by cohort, assay platform, and pre-analytical protocols. These metrics do not constitute performance claims for clinical diagnostic use.

Standard Curve & Linearity

8-point calibration curve with R² ≥ 0.99 across the full dynamic range. Recombinant p-Tau217 calibrator. Dilution linearity verified at 1:2, 1:4, and 1:8 in human EDTA plasma matrix.

Precision & Reproducibility

Intra-plate CV <8% across low, medium, and high QC samples. Inter-plate CV <12%. Three independent QC levels run in duplicate on each plate. Lot-to-lot bridging data available.

Sample Stability

p-Tau217 stable in EDTA plasma for 24 hours at RT, 7 days at 4°C, and ≥2 years at −80°C. Up to 3 freeze-thaw cycles with <10% signal loss. Compatible with EDTA, lithium heparin, and citrate collection tubes.

How MSD S-PLEX Detects p-Tau217 at fg/mL

Why standard immunoassays are insufficient — and how electrochemiluminescence addresses the sensitivity gap for plasma p-Tau217 research.

The Sensitivity Challenge

Plasma p-Tau217 circulates at approximately 0.1–10 pg/mL in individuals without cerebral amyloid pathology and 1–50 pg/mL in those with amyloid deposition. Typical ELISA has an LLOQ of 10–50 pg/mL — insufficient to reliably differentiate these ranges. Even standard multiplex platforms with pg/mL sensitivity cannot consistently quantify p-Tau217 at the lower end of the physiological range.

The S-PLEX Solution

1. High-Capacity Carbon Electrode Surface

MSD's proprietary carbon electrode provides ~10× higher binding capacity than polystyrene, capturing more target molecules per well and extending the measurable range.

2. SULFO-TAG ECL Label

Non-enzymatic, chemically stable label that emits light only upon electrical stimulation at the electrode surface. Zero background from unbound detection antibody or sample autofluorescence.

3. S-PLEX Signal Amplification

An additional antibody amplification layer multiplies the number of SULFO-TAG labels per captured p-Tau217 molecule, pushing the lower limit of detection into the fg/mL range.

4. Electrical Excitation

ECL signal is generated only when voltage is applied to the electrode — no excitation light source means no autofluorescence, light scattering, or photo-bleaching artifacts.

S-PLEX p-Tau217 Assay Specifications

TechnologyMSD S-PLEX (ECL)

Analytep-Tau217 (pT217 Tau)

LOD<0.05 pg/mL (fg/mL)

LLOQ~0.1 pg/mL

Dynamic Range0.1–10,000 pg/mL (5+ logs)

Sample Volume25 µL per well

Recommended MatrixEDTA Plasma

Acceptable MatricesSerum, CSF (on consultation)

Intra-Assay CV<8%

Inter-Assay CV<12%

Plate Format96-well MULTI-ARRAY

Read Time~70 seconds/plate

p-Tau217 vs Other AD Research Biomarkers

Relative strength of association with AD pathology in published cohorts

p-Tau217 5/5

p-Tau231 4/5

p-Tau181 3/5

Aβ42/Aβ40 3/5

GFAP 3/5

NfL 2/5*

* NfL is a non-specific marker of axonal injury. Scores reflect strength of association with Alzheimer's pathology specifically, based on published head-to-head cohort studies. For research reference only.

p-Tau217 Assay Service Details

Service package, sample requirements, and deliverables.

Service Package

Item	Full Service	Kit Only
Sample Processing	Included	— Self-run
Standard Curve	8-point, each plate	Reagents provided
QC Samples	3 levels, duplicate	— User-prepared
Data Analysis	Full report	— Self-analysis
Raw Data	Included	— Instrument-dependent

For Research Use Only. Not for diagnostic procedures.

Sample Submission Requirements

Preferred MatrixEDTA Plasma

AcceptableSerum, CSF (consultation required)

Typical Sample Volume50–200 µL per aliquot depending on panel and replication; as low as 25 µL per well. We'll advise exact requirements.

CollectionEDTA tube → 1,500×g/10 min → aliquot → −80°C

ShippingDry ice, overnight courier

DocumentationSample manifest form (provided)

How to Get Started

Consult

Tell us about your study — samples, timeline, analytes of interest. We'll recommend the optimal panel configuration.

Ship

Send your samples on dry ice. We provide collection kits and customs support for international shipments.

Receive Data

Receive your complete data package — quantitative report, raw data, and publication-ready methods.

New to MSD or testing a hypothesis? Ask about feasibility runs — a small pilot with a subset of samples to verify the assay works in your matrix before committing to a full study.

p-Tau217 Detection: MSD S-PLEX vs Other Platforms

Platform comparison for research applications.

Feature	MSD S-PLEX (ECL)	Simoa (Quanterix)	Conventional ELISA	LC-MS/MS
Sensitivity (LOD)	fg/mL	fg/mL	~10–50 pg/mL	~1–5 pg/mL
Dynamic Range	5–6 logs	4–5 logs	2–3 logs	3–4 logs
Sample Volume	25 µL	~100 µL	100 µL	250–500 µL
Multiplex Capability	Up to 10-plex	Up to 4-plex	Single-plex only	Targeted panels
Throughput	96-well / 70 sec read	~60 samples/hr	96-well batch	Low (~20/day)
Matrix Tolerance	High	Moderate	Low–Moderate	High
Best Research Fit	Cohort studies, trials, multiplex neuro panels	Ultra-low single markers, rare matrices	Small pilot studies	Isoform-specific work

For a detailed head-to-head analysis covering all neuro biomarkers, see our MSD vs Simoa: Ultra-Sensitive Immunoassay Platform Comparison.

What You Receive

Quantitative report — analyte concentrations, QC metrics, standard curve parameters (Excel + PDF)
Raw ECL data — per-well signal values, plate maps, curve plots — analysis-ready formats
Methods summary — ready for manuscript Methods or supplementary materials
QC documentation — intra/inter-plate CV, LOD/LLOQ, dilution linearity verification
Sample tracking log — receipt to analysis chain-of-custody
Consultation — post-delivery call to discuss results and interpretation as needed

Why Our Clients Choose Us

Assay expertise — dedicated scientist assigned to your project, not a rotating team
Flexible delivery — full-service or kit-only; custom U-PLEX combinations available
No-surprise QC — all QC results reported transparently; flagged values with explanations, never silently removed
Publication track record — data generated on our platform appears in peer-reviewed journals
Longitudinal consistency — reagent lot tracking across timepoints for multi-year cohort studies
Direct communication — talk to the scientist running your assay, not a project manager

Supporting Publications

Published research supporting p-Tau217 as a blood-based biomarker for Alzheimer's pathology.

Palmqvist S, Janelidze S, Quiroz YT, et al. (2020) JAMA. 324(8):772–781. "Discriminative Accuracy of Plasma Phospho-tau217 for Alzheimer Disease vs Other Neurodegenerative Disorders." DOI: 10.1001/jama.2020.12134 · PMID: 32722745

Brickman AM, Manly JJ, Honig LS, et al. (2021) Alzheimer's & Dementia. 17(8):1353–1364. "Plasma p-tau181, p-tau217, and other blood-based Alzheimer's disease biomarkers in a multi-ethnic, community study." DOI: 10.1002/alz.12301 · PMID: 33580742

Thijssen EH, La Joie R, Wolf A, et al. (2020) Nature Medicine. 26(3):387–397. "Diagnostic value of plasma phosphorylated tau181 in Alzheimer's disease and frontotemporal lobar degeneration." DOI: 10.1038/s41591-020-0762-2

Ashton NJ, Pascoal TA, Karikari TK, et al. (2021) Acta Neuropathologica. 141(5):709–724. "Plasma p-tau231: a new biomarker for incipient Alzheimer's disease pathology." DOI: 10.1007/s00401-021-02275-6 · PMID: 33585983

Cullen NC, Leuzy A, Palmqvist S, et al. (2021) Nature Communications. 12(1):3555. "Plasma biomarkers of Alzheimer's disease improve prediction of cognitive decline in cognitively unimpaired elderly populations." DOI: 10.1038/s41467-021-23746-0

Janelidze S, Mattsson N, Palmqvist S, et al. (2020) Nature Medicine. 26(3):379–386. "Plasma P-tau181 in Alzheimer's disease: relationship to other biomarkers, differential diagnosis, neuropathology and longitudinal progression to Alzheimer's dementia." DOI: 10.1038/s41591-020-0755-1 · PMID: 32123385

References provided for informational and scientific context. For Research Use Only.

p-Tau217 Assay FAQ

Is this p-Tau217 assay validated for clinical diagnostic use?

No. This p-Tau217 assay is validated for research use only (RUO). It is suitable for preclinical studies, cohort research, biomarker discovery, and therapeutic development applications. It is not validated for clinical diagnostic procedures, patient management decisions, or as a standalone screening tool in a clinical setting. All data is reported with the explicit disclaimer that it should not be used as the sole basis for clinical decision-making.

How much sample volume do I need?

Volume requirements depend on your panel configuration and replication strategy. Typically 50–200 µL of EDTA plasma per aliquot covers most single-plex and small-panel assays. The MSD platform requires as little as 25 µL per well, making it well-suited for volume-limited samples. We recommend discussing your specific sample constraints during study design — we'll help determine the minimum viable volume and advise on an aliquot strategy to maximize your sample inventory.

Why is EDTA plasma the recommended matrix?

EDTA plasma has shown more consistent p-Tau217 measurements across published research studies compared to serum. The clotting process in serum collection may release additional Tau fragments from platelets and blood cells, potentially introducing pre-analytical variability. We recommend consistent matrix use throughout a study. Matrix-specific reference ranges can be provided to support your sample type choice.

Can p-Tau217 be combined with other biomarkers in a multiplex panel?

Yes. Through MSD's U-PLEX custom platform, p-Tau217 can be combined with up to 9 other biomarkers in a single well. Common combinations include: p-Tau217 + NfL + GFAP (neurodegeneration 3-plex), and p-Tau217 + Aβ40 + Aβ42 (AD pathology panel). Note that for maximum sensitivity (fg/mL range), the S-PLEX single-plex format is recommended. Contact us to determine the optimal configuration for your research objectives.

What documentation do you provide for data integrity and reproducibility?

We provide comprehensive documentation with every project: (1) full analytical report including standard curve parameters, QC sample performance, and analyte-by-analyte precision metrics; (2) sample chain-of-custody log from receipt through analysis; (3) instrument run logs with maintenance records; and (4) a detailed methods section suitable for manuscript preparation. Our documentation practices are designed to support data integrity, reproducibility, and peer review. For studies that may later inform regulated work, we recommend discussing documentation requirements with our team during the study design phase so we can align our processes with your downstream needs. All services are provided under a research-use-only framework.

How should I prepare samples for shipping?

Collect blood in EDTA tubes → centrifuge at 1,500×g for 10 minutes at 4°C → transfer plasma to labeled polypropylene cryovials → freeze immediately at −80°C → ship on dry ice via overnight courier. Include a completed sample manifest form. Avoid repeated freeze-thaw cycles. Contact us for a detailed sample collection and shipping guide.

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