MSD S-PLEX · fg/mL Sensitivity

MSD GFAP (Glial Fibrillary Acidic Protein) Assay Service

Quantify Glial Fibrillary Acidic Protein (GFAP) at femtogram-per-milliliter sensitivity — a key marker of astrocyte activation and astrogliosis studied across traumatic brain injury, Alzheimer's disease, and neuroinflammation research.

Unlike neuron-derived markers such as NfL and p-Tau, GFAP reflects glial biology — specifically the astrocyte response to CNS injury. Rapidly released after traumatic brain injury and elevated in Alzheimer's-related astrogliosis, GFAP is a complementary marker for neuroinflammation and neurodegeneration research. MSD S-PLEX delivers the fg/mL sensitivity required to quantify GFAP in both acute and chronic disease settings.

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GFAP — A Key Astrocyte Marker in CNS Research

Glial Fibrillary Acidic Protein (GFAP) is a type III intermediate filament protein expressed primarily in astrocytes of the central nervous system. Under homeostatic conditions, GFAP maintains astrocyte structural integrity and contributes to the blood-brain barrier, synaptic function, and CNS repair processes. Following CNS injury or disease, astrocytes undergo reactive changes — a process known as astrogliosis — characterized by GFAP upregulation and morphological transformation. This makes GFAP a direct window into glial biology, offering complementary information to neuron-derived markers like neurofilament light (NfL) and phosphorylated Tau.

Why GFAP Matters in CNS Research

Astrocyte-specific: GFAP is the canonical marker of mature astrocytes — providing glial-specific information that complements neuron-derived biomarkers (NfL, p-Tau, UCH-L1) for a more complete picture of CNS pathophysiology.
Rapid release in TBI: GFAP is released from injured astrocytes within hours of traumatic brain injury and is one of the most extensively studied blood biomarkers for detecting acute intracranial pathology. Published studies report detectable GFAP elevations within 1–4 hours post-injury.
Astrogliosis in neurodegeneration: Reactive astrogliosis, marked by elevated GFAP, is a neuropathological hallmark of Alzheimer's disease, frontotemporal dementia, and other neurodegenerative conditions — often preceding or paralleling neuronal loss.
Neuroinflammatory conditions: GFAP is a core biomarker in neuromyelitis optica spectrum disorder (NMOSD) research, where astrocyte-targeting autoantibodies (anti-AQP4) drive primary astrocytopathy.
Blood-brain barrier disruption:Serum and plasma GFAP levels can indicate BBB integrity, as GFAP leakage into peripheral circulation increases with barrier compromise in glioblastoma, stroke, and neuroinflammatory conditions.

Research Applications

Traumatic Brain Injury (TBI) research — GFAP is a leading blood biomarker for detecting acute intracranial injury. Quantify GFAP in plasma or serum to study injury severity, time-course of astrocyte response, and correlation with imaging findings in TBI cohorts.
Alzheimer's disease research — investigate astrocyte reactivity and astrogliosis in AD. Plasma GFAP is elevated in preclinical and clinical AD and may reflect glial contributions to amyloid- and Tau-driven neurodegeneration. Combine GFAP with p-Tau217, NfL, and Aβ40/42 for multi-modal CNS biomarker profiling.
Neuromyelitis optica spectrum disorder (NMOSD) research — GFAP is a direct marker of astrocyte damage in NMOSD, where anti-AQP4 IgG targets astrocytes. Published studies report markedly elevated CSF and serum GFAP during acute NMOSD attacks.
Glioblastoma and brain tumor research — GFAP expression patterns help characterize glial tumors. Plasma GFAP may serve as a research biomarker for tumor progression, treatment response, and BBB integrity in glioma studies.
Neuroinflammation and multiple sclerosis research — study astrocyte involvement in MS and other neuroinflammatory conditions. GFAP complements NfL (axonal injury) and cytokine panels for comprehensive neuroinflammatory profiling.

GFAP Assay Performance

Representative performance metrics from peer-reviewed studies using GFAP for CNS injury, neurodegeneration, and neuroinflammation research.

<1 hr

Detectable Post-TBI
GFAP released within 1 hour of injury

2–3×

AD vs. Control Elevation
Plasma GFAP in preclinical/clinical AD

0.85 AUC

TBI Detection Performance
Representative published value

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 human GFAP calibrator. Dilution linearity verified at 1:2, 1:4, and 1:8 in human EDTA plasma, serum, and NHP plasma matrices.

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. Manufacturer-provided controls with assigned target ranges for lot-to-lot consistency.

Sample Stability

GFAP is 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 and lithium heparin plasma, serum, and CSF. Hemolysis may affect measurements — hemoglobin assessment recommended.

How MSD S-PLEX Detects GFAP at fg/mL

Why standard immunoassays are insufficient — and how electrochemiluminescence addresses the sensitivity gap for plasma GFAP research across TBI, neurodegeneration, and neuroinflammation.

The Sensitivity Challenge

Plasma GFAP circulates at very low levels in healthy individuals — typically in the single-digit to low tens of pg/mL range. Following CNS injury or in neurodegenerative conditions, GFAP can rise to tens to hundreds of pg/mL. Conventional ELISA platforms, with typical LLOQs of 10–50 pg/mL, often lack the sensitivity to reliably quantify GFAP at baseline concentrations — making it difficult to establish reference ranges or detect subtle elevations in early disease stages. The MSD S-PLEX platform overcomes this limitation with femtogram-level sensitivity, enabling detection across the full pathophysiological range — from low-normal baseline to acute post-injury peaks.

The S-PLEX Solution

1. High-Capacity Carbon Electrode Surface

MSD's proprietary carbon electrode provides ~10× higher binding capacity than polystyrene, capturing more GFAP 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 GFAP molecule, pushing the lower limit of detection into the fg/mL range — critical for detecting low-baseline GFAP in healthy control cohorts.

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. This is particularly advantageous for plasma samples where matrix autofluorescence can compromise fluorescence-based readouts.

S-PLEX GFAP Assay Specifications

TechnologyMSD S-PLEX (ECL)

AnalyteGFAP (Glial Fibrillary Acidic Protein)

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, NHP Plasma

Intra-Assay CV<8%

Inter-Assay CV<12%

Plate Format96-well MULTI-ARRAY

Read Time~70 seconds/plate

GFAP vs Complementary CNS Biomarkers

Relative utility for different CNS research applications — GFAP reflects glial biology, complementing neuron-derived and pathology-specific markers

GFAP 5/5

p-Tau217 4/5

NfL 4/5

UCH-L1 3/5

S100B 3/5

Aβ42/Aβ40 2/5*

* Aβ42/Aβ40 is an Alzheimer's pathology marker with limited direct relevance to astrocyte biology. Scores reflect overall utility across TBI, neurodegeneration, and neuroinflammation research — GFAP uniquely captures astrocyte responses that are invisible to neuron-specific and pathology-specific markers. For research reference only.

GFAP 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, NHP Plasma (consultation recommended)

Typical Sample Volume50–200 µL per aliquot; as low as 25 µL per well. We'll advise based on your panel.

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.

Testing a hypothesis or new to this assay? Ask about a pilot feasibility run with a subset of samples before committing to a full study.

GFAP 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 GFAP as a biomarker of astrocyte activation in CNS injury and disease.

Abdelhak A, Foschi M, Abu-Rumeileh S, et al. (2022) Nature Aging. 2(11):1040–1053. "Blood GFAP as an emerging biomarker in brain disorders." DOI: 10.1038/s43587-022-00316-3

Benedet AL, Milà-Alomà M, Vrillon A, et al. (2021) JAMA Neurology. 78(12):1471–1483. "Differences Between Plasma and Cerebrospinal Fluid Glial Fibrillary Acidic Protein Levels Across the Alzheimer Disease Continuum." DOI: 10.1001/jamaneurol.2021.3671 · PMID: 34661615

Bazarian JJ, Biberthaler P, Welch RD, et al. (2018) JAMA Neurology. 75(4):429–437. "Serum GFAP and UCH-L1 for prediction of absence of intracranial injuries on head CT (ALERT-TBI)." DOI: 10.1001/jamaneurol.2017.4460

Papa L, Brophy GM, Welch RD, et al. (2016) JAMA Neurology. 73(5):551–560. "Time Course and Diagnostic Accuracy of Glial and Neuronal Blood Biomarkers GFAP and UCH-L1 in a Large Cohort of Trauma Patients With and Without Mild Traumatic Brain Injury." DOI: 10.1001/jamaneurol.2016.0039 · PMID: 27018834

Watanabe M, Nakamura Y, Michalak Z, et al. (2019) Neurology: Neuroimmunology & Neuroinflammation. 6(4):e575. "Serum GFAP and neurofilament light as biomarkers of disease activity and disability in NMOSD." DOI: 10.1212/NXI.0000000000000575

Oeckl P, Halbgebauer S, Anderl-Straub S, et al. (2019) Molecular Psychiatry. 24(10):1463–1471. "Glial Fibrillary Acidic Protein in Serum is Increased in Alzheimer's Disease and Correlates with Cognitive Impairment." DOI: 10.1038/s41380-019-0418-0

References for informational context. For Research Use Only.

GFAP Assay FAQ

Is this GFAP assay validated for clinical diagnostic use?

No. This GFAP assay is manufacturer-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.

Why is GFAP considered an astrocyte-specific marker, and how does it complement NfL and p-Tau?

GFAP is the principal intermediate filament protein of mature astrocytes and is not expressed by neurons, oligodendrocytes, or microglia under normal conditions — making it highly specific to the astrocyte lineage. In contrast, NfL is released from injured axons (neuron-specific but not cell-type-specific within neurons), and p-Tau reflects a specific pathological process (tau hyperphosphorylation). Combining GFAP with NfL and/or p-Tau217 provides a multi-cellular view of CNS pathophysiology: GFAP reports on astrocyte reactivity, NfL on axonal injury, and p-Tau on AD-specific tau pathology. This multi-marker approach is increasingly used in neurodegeneration and TBI research to capture complementary aspects of CNS injury and disease.

What is the minimum sample volume required for GFAP analysis?

We require a minimum of 50-200 .L of EDTA plasma is typical for most assays. Exact requirements depend on your panel configuration and replication needs — we'll help determine the minimum viable volume during study design CSF requires only 25 µL. NHP plasma volumes follow the same guidelines.

Which sample matrix is recommended for GFAP — plasma or serum?

EDTA plasma is recommended as the primary matrix, based on published literature showing consistent GFAP measurements and established specimen-handling protocols in both TBI and neurodegeneration research. Serum is also an acceptable matrix and has been widely used in TBI biomarker studies (notably the ALERT-TBI study). However, the clotting process may release GFAP from platelets or other blood cells, potentially introducing pre-analytical variability. We strongly recommend using the same matrix consistently throughout a given study. If serum must be used, we can provide matrix-specific reference data to support interpretation. CSF is also compatible for studies requiring paired CSF-plasma analysis.

Can GFAP be combined with other CNS biomarkers in a multiplex panel?

Yes. Through MSD's U-PLEX custom platform, GFAP can be combined with up to 9 other biomarkers in a single well. Common combinations for CNS research include: GFAP + NfL + UCH-L1 (TBI/neurotrauma panel), GFAP + NfL + p-Tau217 (neurodegeneration 3-plex), and GFAP + NfL + Aβ40 + Aβ42 (AD pathology plus glial panel). Note that for maximum sensitivity (fg/mL range), the S-PLEX single-plex format is recommended for each individual analyte. Contact us to determine the optimal configuration for your research objectives, balancing multiplex convenience against single-plex sensitivity.

How should I prepare and ship samples for GFAP analysis?

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 (limit to ≤3). For TBI studies requiring rapid sample processing, we recommend documenting the exact time from injury to blood draw, as GFAP levels change dynamically in the acute post-injury period. Contact us for a detailed sample collection and shipping guide tailored to your study design.

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