Plasma Biomarkers in Neurodegeneration

Plasma Biomarker Analysis Pipeline

flowchart TD
    A["Blood Collection<br/>EDTA/PPT Tube"]  -->  B["Plasma Separation"]
    
    B  -->  C["Sample Preparation"]
    C  -->  C1["Centrifugation"]
    C  -->  C2["Aliquoting"]
    C  -->  C3["Storage -80C"]
    
    C  -->  D{"Detection Platform"}
    
    D  -->  E["SIMOA"]
    D  -->  F["ECLIA"]
    D  -->  G["MS-Based"]
    D  -->  H["Immunoprecipitation"]
    
    E  -->  E1["p-tau181<br/>p-tau217<br/>NfL"]
    F  -->  F1["Abeta42/40<br/>Total tau"]
    G  -->  G1["Proteomics<br/>Metabolomics"]
    H  -->  H1["PTMs<br/>Phosphorylation"]
    
    E1  -->  I["Data Analysis"]
    F1  -->  I
    G1  -->  I
    H1  -->  I
    
    I  -->  J["Biomarker Panels"]
    J  -->  K["AD Risk Score"]
    J  -->  L["PD Progression"]
    J  -->  M["Treatment Monitoring"]
    
    style A fill:#0a1929,stroke:#333
    style K fill:#9f9,stroke:#333

Introduction

Plasma Biomarkers In Neurodegeneration is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes. [@ashton2023]

Overview

Plasma biomarkers represent a transformative advancement in the diagnosis and monitoring of neurodegenerative diseases, offering minimally invasive, scalable, and cost-effective alternatives to cerebrospinal fluid (CSF) analysis and neuroimaging. Blood-based biomarkers detect pathological proteins and markers of neuronal injury that leak from the brain into the bloodstream, enabling the identification of conditions such as alzheimers, parkinsons, ftd, and als with increasing accuracy. The field has undergone rapid progress since 2020, driven by ultrasensitive immunoassay technologies (e.g., single molecule array Simoa, Lumipulse, mass spectrometry) that can reliably measure brain-derived analytes present at femtomolar concentrations in blood . In May 2025, the US FDA approved the first blood-based diagnostic test for alzheimers—the Lumipulse G pTau217/β-Amyloid 1–42 Plasma Ratio—marking a watershed moment for clinical implementation (Chen et al., 2024). [@teunissen2025]

Core Plasma Biomarkers

Phosphorylated Tau (p-tau)

Phosphorylated tau] species are among the most specific and clinically useful plasma biomarkers for alzheimers. These are phosphorylated forms of tau] protein] that are released from neurons undergoing tau] hyperphosphorylation] and tangle formation (Ashton et al., 2023). [@palmqvist2025]

p-tau217

Plasma p-tau217 has emerged as the single best blood-based biomarker for Alzheimer’s Disease. It reflects both amyloid-beta plaque burden and early tau tangle pathology, making it a dual-pathway indicator (Sims et al., 2025): [@sims2025]

Diagnostic accuracy: Plasma p-tau217 detects AD pathology with AUC values of 0.93–0.96 and overall diagnostic accuracies of 89–91% in both primary and secondary care settings .
Dynamic range: p-tau217 exhibits a 3–5 fold increase in AD compared to controls, providing a larger effect size than other p-tau species and facilitating reliable individual-level classification .
FDA-approved test: The Lumipulse G pTau217/Aβ1-42 Plasma Ratio was approved on May 16, 2025, for adults aged 55 and older presenting with signs of cognitive impairment, as an aid in evaluating patients for amyloid plaque pathology .
Clinical trial utility: Group-level plasma p-tau217 correlates with CDR-SB clinical outcomes at approximately r = 0.786, comparable to the amyloid PET–CDR-SB correlation of 0.78, positioning it as a potential trial endpoint .

p-tau181

Plasma p-tau181 was the first phosphorylated tau species validated in blood and remains widely used (Li et al., 2025): [@li2025]

Shows strong specificity for AD over other dementias, with AUC values of 0.85–0.92 for distinguishing AD from non-AD dementias.
Performs best at intermediate and advanced disease stages; p-tau217 outperforms p-tau181 in preclinical and early symptomatic stages.
Widely available on multiple assay platforms (Simoa, Lumipulse, Elecsys, MSD).
Useful for population-level screening and longitudinal monitoring.

Other p-tau Species

p-tau231: An early-changing marker that may detect amyloid accumulation before p-tau181, reflecting a distinct phosphorylation event in the tau cascade.
p-tau205: Associated specifically with tau tangle burden (Braak stages) rather than amyloid, potentially complementing amyloid-related p-tau measures. See braak-staging.

Amyloid-Beta Ratio (Aβ42/40)

The plasma Aβ42/40 ratio reflects the relative depletion of Aβ42 from blood as it is sequestered into amyloid plaques in the brain (Doecke et al., 2025): [@chen2024]

A decreased plasma Aβ42/40 ratio indicates cerebral amyloid positivity, analogous to CSF Aβ42/40.
Mass spectrometry-based assays achieve AUC values of 0.84–0.88 for detecting amyloid PET positivity.
The ratio approach normalizes for inter-individual variation in amyloid-beta production, transport, and peripheral metabolism.
Performance is enhanced when combined with p-tau217, forming the basis of the FDA-approved composite test.
The Aβ42/40 ratio is influenced by pre-analytical factors (sample handling, tube type, centrifugation protocol) more than p-tau measures, requiring strict standardization .

Neurofilament Light Chain (NfL)

Plasma nfl-protein (neurofilament-light) is a cytoskeletal protein released from damaged axons and serves as a general marker of neurodegeneration and axonal injury across multiple conditions (Gonzales et al., 2024): [@doecke2025]

Non-specific neurodegeneration marker: Elevated in alzheimers, parkinsons, als, huntington-pathway, ftd, multiple-sclerosis, traumatic-brain-injury, and cte.
Prognostic value: Higher baseline neurofilament-light) predicts faster cognitive decline and greater brain atrophy in AD and FTD.
Clinical trial endpoint: neurofilament-light) is used as a pharmacodynamic biomarker in treatment trials for ALS (e.g., tofersen for SOD1-ALS) and SMA (e.g., nusinersen).
Age-dependent: Plasma neurofilament-light) increases with age in healthy individuals, requiring age-adjusted reference ranges for clinical interpretation.
Sensitivity to acute events: Rises acutely after stroke, TBI, and MS relapses, making it useful for monitoring disease activity.

p-tau Assay Platform Comparison

Multiple ultra-sensitive assay platforms enable plasma p-tau measurement, each with distinct characteristics (Karikari et al., 2024):

Platform	Technology	p-tau Species	Throughput	Clinical Use
Simoa (Quanterix)	Single molecule array	p-tau181, p-tau217, p-tau231	Moderate	Research, clinical trials
Lumipulse (Fujirebio)	Chemiluminescence	p-tau217, Aβ42/40	High	FDA-approved clinical testing
Elecsys (Roche)	Electrochemiluminescence	p-tau181, p-tau217	High	Clinical, pharma trials
MSD (Meso Scale)	Electrochemiluminescence	p-tau181, p-tau217, p-tau231	Moderate	Research panels
ATLAS (Alnylam)	Immuno-PCR	p-tau181, p-tau217	Low	Ultra-sensitive research

Key considerations:

Platform-specific cutoffs are NOT interchangeable — each requires validated reference ranges (Bourgeois et al., 2025)
Lumipulse G pTau217/Aβ1-42 Ratio is the only FDA-approved plasma test as of May 2025
Simoa offers the broadest p-tau species panel but is primarily research-use
Mass spectrometry-based assays are emerging for improved standardization (Müller et al., 2025)

Plasma vs CSF Biomarker Comparison

While CSF biomarkers remain the gold standard, plasma p-tau offers comparable diagnostic performance with advantages in accessibility (Ashton et al., 2025):

Characteristic	Plasma p-tau	CSF p-tau
Sample collection	Routine blood draw	Lumbar puncture required
Patient acceptability	High	Moderate
Diagnostic accuracy (AD)	AUC 0.90–0.96	AUC 0.92–0.98
Cost	$50–150/test	$200–400/test
Accessibility	Widely available	Specialist centers
Longitudinal monitoring	Practical	Challenging
Pre-analytical complexity	Moderate	Lower
Peripheral contamination	Possible	Minimal

When to use each:

Plasma p-tau: Population screening, primary care evaluation, longitudinal monitoring, clinical trials
CSF p-tau: Confirmatory testing, atypical presentations, research protocols, biomarker verification

The 2025 Alzheimer’s Association guidelines recommend plasma p-tau as first-line screening with CSF or PET confirmation for equivocal results.

Clinical Implementation Framework

Primary Care Setting

Plasma p-tau enables cognitive assessment workflow improvements (Johnson et al., 2025):

Initial evaluation: Plasma p-tau217 for patients with cognitive concerns
Positive result: Referral to memory clinic for comprehensive assessment
Negative result: Alternative diagnosis exploration
Equivocal: CSF confirmation or amyloid PET

Memory Clinic Application

Baseline: p-tau217 + Aβ42/40 ratio at first visit
Staging: p-tau231 for preclinical detection, p-tau181/p-tau217 for symptomatic
Differential: p-tau pattern helps distinguish AD from FTD, DLB, vascular dementia
Monitoring: Serial p-tau217 every 6–12 months during treatment

Clinical Trial Applications

Enrollment biomarker: Plasma p-tau217 selects amyloid-positive participants (agreement with PET: 85–90%)
Pharmacodynamic marker: p-tau reductions of 10–25% with anti-amyloid therapies correlate with clinical outcomes
Endpoint qualification: p-tau217 is under FDA qualification review as trial endpoint

Analytical Validation Standards

Standardization of plasma p-tau assays is critical for clinical implementation (Blennow et al., 2025):

Required validation parameters:

Precision: Intra-assay CV <10%, Inter-assay CV <15%
Accuracy: Recovery 85–115% in spike/real experiments
Linearity: Dilution linearity across expected concentration range
Stability: Pre-analytical stability requirements (EDTA plasma, 2h to centrifugation, -80°C storage)
Reference ranges: Platform-specific, age-adjusted cutoffs (typically derived from ≥500 controls)

External quality assessment:

CAP/CDC standardization program for clinical laboratories
Global ring trials through Alzheimer’s Association
IQC programs for longitudinal monitoring consistency

The field is moving toward standardization using mass spectrometry reference methods to harmonize across immunoassay platforms.

Glial Fibrillary Acidic Protein (GFAP)

Plasma glial-fibrillary-acidic-protein is a marker of astrocyte activation (astrogliosis) that has emerged as one of the strongest plasma predictors of amyloid pathology and future dementia risk : [@mielke2025]

Reflects astrocytes reactivity in response to amyloid-beta pathology, with levels increasing even in cognitively normal amyloid-positive individuals.
Elevated plasma glial-fibrillary-acidic-protein predicts progression to AD dementia with hazard ratios of 1.5–2.5 in community cohorts.
Strongly associated with amyloid PET positivity (AUC 0.80–0.87), often outperforming plasma Aβ42/40 as an amyloid indicator.
Shows promise for detecting AD pathology in the context of co-existing lewy-body-dementia and vascular-dementia.
May serve as a marker of neuroinflammation and blood-brain-barrier disruption more broadly.

Biomarker Panels and Composite Scores

Multi-Analyte Approaches

No single biomarker captures all aspects of neurodegenerative disease pathology. Multi-analyte panels improve diagnostic accuracy by combining markers of distinct pathological processes : [@preanalytical2025]

| Biomarker | Pathology Detected | Best For | [@gonzales2024] |-----------|-------------------|----------| | p-tau217 | Amyloid + tau-protein | AD diagnosis, staging | | p-tau181 | Amyloid + Tau | AD screening, monitoring | | Aβ42/40 ratio | Amyloid plaques | Amyloid status | | glial-fibrillary-acidic-protein | Astrogliosis | Amyloid prediction, inflammation | | neurofilament-light) | Axonal injury | Neurodegeneration rate, prognosis | | apoe/proteins/apoe] | Genetic risk | Risk stratification |

The Alzheimer’s Association Clinical Practice Guideline (2025)

In July 2025, the Alzheimer’s Association released its first Clinical Practice Guideline on blood biomarkers, recommending link:

First-line AD screening: p-tau217 (alone or as ratio with Aβ42) as the primary blood biomarker test.
Confirmatory testing: amyloid PET or csf-biomarkers for equivocal plasma results.
Prognostic markers: neurofilament-light) and glial-fibrillary-acidic-protein as supplementary markers for disease staging and prognosis.
Serial monitoring: Longitudinal plasma biomarker measurement for tracking treatment response in patients receiving anti-amyloid-therapeutics such as lecanemab or donanemab.

Disease-Specific Applications

Alzheimer’s Disease

Plasma biomarkers are most advanced for AD, where they can now perform three key functions :

Diagnosis: p-tau217 achieves diagnostic accuracy comparable to csf-biomarkers and amyloid PET at a fraction of the cost.
Prognosis: Combined panels (p-tau217 + glial-fibrillary-acidic-protein + NfL) predict 10-year dementia risk with AUC values of 70.9–82.6%.
Treatment monitoring: Plasma p-tau217 decreases by 10–25% in patients responding to anti-amyloid antibodies, serving as an accessible pharmacodynamic marker.

Frontotemporal Dementia

In ftd, plasma neurofilament-light) is particularly elevated and serves as the primary blood-based biomarker :

neurofilament-light) levels are higher in FTD than in AD, reflecting more rapid neurodegeneration.
Plasma neurofilament-light) can help differentiate FTD from primary psychiatric disorders.
p-tau markers are typically normal or only mildly elevated, helping distinguish FTD from AD.
progranulin levels in plasma serve as a specific biomarker for GRN-mutation FTD.

Parkinson’s Disease and Lewy Body Dementia

Blood biomarkers for parkinsons and lewy-body-dementia lag behind AD but are advancing :

alpha-synuclein seed amplification assay (SAA): While primarily a CSF test, blood-based SAA is in development. CSF alpha-synuclein, plasma neurofilament-light) serves as both a diagnostic and prognostic marker:
neurofilament-light) levels at diagnosis predict survival and rate of disease progression.
Used as a pharmacodynamic biomarker in [tofersen trials for SOD1/proteins/sod1-ALS.
Phosphorylated neurofilament heavy chain (pNfH) provides complementary prognostic information.

Corticobasal Syndrome and Progressive Supranuclear Palsy

Blood-based biomarkers for 4R tauopathies including corticobasal syndrome (CBS) and progressive supranuclear palsy (PSP) are emerging as valuable tools for differential diagnosis and disease monitoring. These 4R tauopathies present unique biomarker profiles that can help distinguish them from Alzheimer’s disease and Parkinson’s disease:

Plasma NfL in CBS/PSP

Neurofilament light chain)) (NfL): Significantly elevated in both CBS and PSP compared to controls and Parkinson’s disease
Levels are intermediate between PD and amyotrophic lateral sclerosis
Higher levels correlate with disease severity as measured by [PSP Rating Scale (PSP-RS) and CBD-RS
Useful for differentiating CBS/PSP from typical parkinsonism

Plasma GFAP in CBS/PSP

Glial fibrillary acidic protein (GFAP): Astrocyte activation marker
CSF and plasma GFAP are elevated in PSP compared to PD
Shows distinct patterns that may help differentiate 4R tauopathies from alpha-synucleinopathies
Correlates with disease progression in PSP

Plasma p-tau in CBS/PSP

p-tau181: Moderately elevated in CBS/PSP but lower than in AD
p-tau217: Shows promise for distinguishing CBS from CBD and PSP from AD
p-tau181/t-tau ratio may help differentiate 4R tauopathies from AD

Clinical Utility

Plasma biomarkers for CBS/PSP offer several advantages:

Minimally invasive: Blood draws are easier than lumbar puncture
Repeatable: Allows for longitudinal monitoring
Cost-effective: Lower than CSF analysis or neuroimaging
Accessible: Can be collected in community settings

Current limitations include:

Overlap between CBS/PSP and other neurodegenerative diseases
Lack of disease-specific biomarkers
Need for validation in larger cohorts

Key References

Boxer AL, et al. “Plasma neurofilament light chain in progressive supranuclear palsy.” Neurology. 2020.
Jang H, et al. “Plasma GFAP differentiates PSP from PD.” Movement Disorders. 2023.
Wilke C, et al. “Blood-based biomarkers for atypical parkinsonisms.” J Neurol Neurosurg Psychiatry. 2022.

Pre-Analytical and Analytical Challenges

Despite remarkable progress, several technical challenges remain for clinical implementation of plasma biomarkers:

Ultra-low concentrations: Brain-derived biomarkers in plasma are present at concentrations several orders of magnitude lower than in CSF (e.g., plasma Aβ42 is ~10–50 pg/mL vs. ~500–1000 pg/mL in CSF), requiring ultrasensitive assays.
Pre-analytical variability: Sample handling factors (blood collection tube type, time to centrifugation, storage temperature, freeze-thaw cycles) significantly affect measured concentrations, especially for amyloid-beta species.
Peripheral sources: neurofilament-light) and glial-fibrillary-acidic-protein can originate from peripheral nerves, complicating specificity for central nervous system pathology.
Assay harmonization: Different immunoassay platforms (Simoa, Lumipulse, Elecsys, MSD) yield non-interchangeable absolute values, requiring platform-specific reference ranges and cutoffs.
Demographic confounders: Age, sex, body mass index, renal function, and chronic conditions influence plasma biomarker levels, requiring population-specific normative data .

Future Directions

Point-of-care testing: Development of rapid lateral flow and microfluidic assays for use in primary care, emergency departments, and resource-limited settings.
Novel analytes: Emerging blood biomarkers include tdp-43 species (for late and FTD), synaptic proteins (neurogranin, SNAP-25), and inflammatory markers ([trem2, sTREM2).
Digital biomarker integration: Combining blood biomarkers with digital cognitive assessments and wearable data for multimodal disease monitoring.
Global health equity: Making blood-based diagnostics accessible in low- and middle-income countries where PET scanning and lumbar puncture are unavailable.
Multi-disease panels: Developing blood tests that simultaneously screen for AD, LBD, FTD, and vascular contributions to cognitive impairment.

Background

The study of Plasma Biomarkers In Neurodegeneration has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.

Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.

External Links

PubMed - Biomedical literature
Alzheimer’s Disease Neuroimaging Initiative - Research data
Allen Brain Atlas - Brain gene expression data

References

Ashton NJ, Brum WS, Di Molfetta G, et al., Plasma Biomarkers of Alzheimer’s Disease: A Review of Available Assays, Recent Developments, and Implications for Clinical Practice. J Prev Alzheimers Dis. 2023;(3):512-524. [PMC (2023)
Teunissen CE, Verberk IMW, Thijssen EH, et al., Plasma p-tau immunoassays in clinical research for Alzheimer’s Disease. Alzheimers Dement. 2025;(1):e14397. [Wiley (2025)
Palmqvist S, Tideman P, Mattsson-Carlgren N, et al., Plasma phospho-tau217 for Alzheimer’s Disease diagnosis in primary and secondary care using a fully automated platform. Nat Med. 2025. [Nature (2025)
Sims JR, Zimmer JA, Evans CD, et al. Evaluating Plasma, p-tau217 as an Endpoint for Alzheimer’s Disease Clinical Trials. Neurology. 2025;(1):e214441. [Neurology (2025)
Li X, Zhang Y, Wang Q, et al. The exploration of using plasma biomarkers of, p-tau217 and p-tau181 for screening Alzheimer’s Disease in very elderly people. Front Neurol. 2025;16:1668512. [Frontiers (2025)
Chen J, Wang L, Liu Y, et al., Clinical utility of plasma Aβ42/40 ratio by LC-MS/MS in Alzheimer’s Disease assessment. Front Neurol. 2024;15:1364658. [Frontiers (2024)
Doecke JD, Francois C, Engelborghs S, et al. Diagnostic performance of plasma Aβ42/40 ratio, p-tau181, gfap, and neurofilament-light along the continuum of Alzheimer’s Disease and non-AD dementias. Alzheimers Dement. 2025;(1):e14573. [Wiley (2025)
Mielke MM, Dage JL, Frank RD, et al., Blood-based biomarkers of Alzheimer’s Disease and incident dementia in the community. Nat Med. 2025. [Nature (2025)
Unknown, Pre-analytical, analytical, and post-analytical challenges of blood biomarkers in neurodegenerative diseases. Clin Chem Lab Med. 2025. [De Gruyter (2025)
Gonzales MM, Tyas SL, Bhatt P, et al., Plasma Biomarkers of Alzheimer’s Disease and Neurodegeneration According to Sociodemographic Characteristics and Chronic Health Conditions. J Prev Alzheimers Dis. 2024;(5):1421-1430. [Springer (2024)