pTau 217: A Blood Biomarker for Alzheimer’s Disease Pathology
pTau 217 (phosphorylated tau at threonine 217) is a highly specific blood-based biomarker of brain amyloid β pathology. Validated against PET imaging and CSF Aβ42/40, it has demonstrated high sensitivity and specificity for identifying amyloid positivity, often outperforming other plasma markers such as pTau181 or Aβ42/40. These properties make pTau 217 a valuable tool for early detection, noninvasive screening, and disease tracking in diagnostic research, therapeutic trials, and longitudinal studies for AD.
While most pTau 217 assays measure a broader population of circulating pTau 217 species, the SPEAR TrueDetect™ epTau 217 Assay measures a distinct subset defined by phosphorylation at threonine 217 and the absence of phosphorylation at serine 199.
Greater AD–Control Discrimination in the Tested Cohort
SPEAR TrueDetect epTau 217 and an N-terminal pTau 217* assay were evaluated in venous plasma from 50 controls and 25 individuals with Alzheimer’s disease. In the tested cohort, epTau 217 achieved an AUC of 0.978, compared with 0.871 for the N-terminal pTau 217 assay.
These results demonstrate that the two assays captured different pTau 217 signal profiles and that epTau 217 provided greater separation between the tested groups. Additional studies are needed to confirm these findings in independent cohorts.
*The internal SPEAR N-terminal pTau 217 assay was created for investigational purposes.
SPEAR TrueDetect epTau 217 achieved an AUC of 0.978, compared with 0.871 for an investigational N-terminal pTau 217 assay. Both assays were evaluated in venous plasma from 50 controls and 25 individuals with Alzheimer’s disease.
Consistent epTau 217 Measurement Across Venous and Capillary Plasma
Capillary blood collection may provide a more accessible approach for decentralized and remote Alzheimer’s disease biomarker research. However, researchers need to understand how biomarker measurements from capillary samples compare with conventional venous samples.
In a paired-sample study, SPEAR TrueDetect epTau 217 demonstrated consistent measurements between venous and capillary samples under the conditions evaluated.
SPEAR TrueDetect epTau 217 demonstrated strong correlation between paired venous and Tasso+ capillary plasma, unlike the investigational N-terminal pTau 217 assay. Paired samples from 15 donors were measured using 1 µL of diluted plasma.
Highly Specific Plasma pTau 217 Measurement with SPEAR epTau 217
The SPEAR epTau 217 assay has demonstrated unparalleled specificity in differentiating Alzheimer’s disease and non-AD patient samples. Combined with its sensitivity and precision (quantifying 100% of healthy samples above fLLOQ), SPEAR epTau 217 offers researchers a powerful tool to better characterize blood based samples in Alzheimer’s research.
In a study to demonstrate SPEAR epTau 217 performance, CSF- and PET-confirmed Alzheimer’s Disease (AD) and non-AD samples were both tested. In this combined cohort study, SPEAR epTau 217 demonstrated a 5.41x mean fold-difference between groups and area under the curve (AUC) of 0.989 for CSF-confirmed samples and 0.984 for PET-confirmed samples. This level of differentiation and predictive power highlights the SPEAR epTau 217 assay in its ability to classify Alzheimer’s and non-Alzheimer’s patient plasma samples.
SPEAR epTau 217 demonstrated a 5.41-fold mean difference between AD and control samples across CSF- and amyloid PET–confirmed cohorts.
SPEAR epTau 217 distinguished AD from control samples with AUCs of 0.989 in the CSF-confirmed cohort and 0.984 in the amyloid PET–confirmed cohort.
Assay Specifications
| MRD | 4X |
| Diluted Sample Volume | 1µL |
| Neat Sample Volume | 10µL |
| fLLOD (fg/mL) | 27.1 |
| fLLOQ (fg/mL) | 44.5 |
| Spike-recovery (% recovery) | 110% |
| Linearity (% recovery) | 93.1% |
| Intra-plate CV (AVG%) | 4.0% |
| Inter-plate CV (AVG%) | 4.0% |
| EDTA Plasma Quantifiability | 100% |
The SPEAR pTau 217 blood test was awarded FDA Breakthrough Device Designation in January 2025, recognizing its potential to transform Alzheimer’s disease (AD) diagnosis. This innovative blood test for pTau 217 offers a less invasive and more accessible alternative to traditional methods like Mass Spectrometry, PET scans and CSF analysis. Designed to detect plasma pTau 217—a core biomarker for Alzheimer’s—the test delivers the sensitivity and specificity needed to accurately measure low concentrations in blood. By supporting research into earlier and more reliable diagnosis, the pTau217 biomarker assay shows strong potential to help distinguish Alzheimer’s from other neurological conditions and expand patient access to timely interventions and emerging therapies.
Supporting Alzheimer’s Disease Research at Any Scale
Whether you’re investigating biomarker dynamics in mild cognitive impairment (MCI) patients or tracking treatment response in longitudinal studies, the SPEAR epTau217 blood test offers robust, reproducible data that aligns with established CSF biomarkers and amyloid PET imaging. By minimizing invasiveness and complexity, the assay is ideal for:
- Multi-marker strategies (e.g., with pTau231 or neurofilament light)
- Clinical trial endpoints and cohort enrichment
- Preclinical screening of candidate therapeutics
- Integration with exploratory pipelines
Recommended for Research Across Sample Types and Research Settings
The SPEAR epTau217 assay is intended for Research Use Only (RUO) and is designed for use with plasma samples. Its unparalleled specificity makes it well-suited for a wide range of research applications, including those involving memory clinic cohorts and therapeutic development studies. The assay’s exceptional analytical performance supports investigation of biomarker trajectories, Aβ positivity, and cognitive decline—offering a scalable alternative to Mass Spectrometry, ELISA- or PET-based methods in Alzheimer’s disease research.
Designed for Sensitivity and Specificity Without Compromise
Researchers seeking performance without operational complexity will appreciate the SPEAR platform’s elegant assay design. SPEAR’s two-factor authentication mechanism and homogeneous format ensure that each pTau217 molecule in a sample is independently verified twice, eliminating false positives and ensuring highly-specific measurement of plasma pTau217 levels, even in challenging blood matrices.
The assay works with samples of 1 µL of diluted sample, enabling repeated analysis from scarce or precious specimens—such as those collected in longitudinal neurodegeneration studies.
From Evaluation to Disease-Modifying Therapy Development
Whether you’re researching biomarkers for Alzheimer’s disease, exploring tau protein kinetics, or validating candidate disease-modifying therapies, the robust SPEAR TrueDetect™ epTau 217 assay kit empowers you to move forward with confidence that comes from results with unparalleled sensitivity, specificity, and precision. The assay’s simplicity makes it a practical tool for research labs of all sizes, aiding the advancement of research from the bench to the clinic.
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