GFAP (Glial fibrillary acidic protein)

Glial fibrillary acidic protein is the principal intermediate filament of mature astrocytes and a marker of reactive astrogliosis. Ultrasensitive immunoassays allow measurement in plasma, where concentrations rise across the Alzheimer disease continuum and are detectable in preclinical, amyloid-positive but cognitively unimpaired individuals. Plasma GFAP discriminates amyloid-PET positive from negative status with higher accuracy than cerebrospinal fluid GFAP and is being evaluated as a complement to amyloid- and tau-specific markers within the ATN framework, where it is sometimes incorporated as an inflammation or astrocyte axis. GFAP also rises in traumatic brain injury, where it is used clinically alongside UCH-L1 for triage. It is not Alzheimer-specific and should be interpreted alongside p-tau217 and amyloid biomarkers.