# GFAP (Glial fibrillary acidic protein)

GFAP (glial fibrillary acidic protein) is the main structural fiber inside mature astrocytes. (Astrocytes are a type of brain support cell.) It is a marker of 'reactive astrogliosis'. That just means astrocytes are responding to injury. Ultra-sensitive assays now let labs measure GFAP in your blood plasma. There, it rises across the Alzheimer's continuum. It is even detectable early, in people who are amyloid-positive but still cognitively normal. Plasma GFAP separates amyloid-PET-positive from negative status. It does so more accurately than spinal-fluid GFAP. It is being tested as a complement to amyloid and tau markers, within the ATN framework. GFAP also rises after a traumatic brain injury. There, it is used clinically (with UCH-L1) for triage. But it is not specific to Alzheimer's. So read it alongside p-tau217 and amyloid biomarkers.

## Sources

- Benedet AL, Mila-Aloma M, Vrillon A, Ashton NJ, Pascoal TA, Lussier F, et al.. (2021). Differences Between Plasma and Cerebrospinal Fluid Glial Fibrillary Acidic Protein Levels Across the Alzheimer Disease Continuum. JAMA Neurology. https://doi.org/10.1001/jamaneurol.2021.3671
- Pereira JB, Janelidze S, Smith R, Mattsson-Carlgren N, Palmqvist S, Teunissen CE, et al.. (2021). Plasma GFAP is an early marker of amyloid-beta but not tau pathology in Alzheimer's disease. Brain. https://doi.org/10.1093/brain/awab223

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_Canonical: https://longevity-switzerland.com/en/glossary/gfap · Part of Longevity Cities · Updated 2026-06-22_