Glial Fibrillary Acidic Protein (GFAP) is a structural protein found almost exclusively in astrocytes, a specialized type of glial cell that supports and protects neurons in the brain and spinal cord. Astrocytes help maintain the blood-brain barrier, support nerve cell repair, regulate inflammation in the brain, and maintain normal brain metabolism.
When brain cells are stressed, injured, inflamed, or degenerating, GFAP can be released into the bloodstream, making it a useful biomarker for evaluating brain injury, neurological inflammation, and disorders affecting the central nervous system (CNS).
Why is GFAP measured?
This marker is often measured to help:
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Detect brain injury or concussion
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Evaluate neuroinflammatory conditions
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Support assessment of neurodegeneration
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Distinguish neurological causes of symptoms like headache, memory changes, confusion, or dizziness
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Provide additional diagnostic data alongside other neuro-injury markers (e.g., UCH-L1, NFL, tau)
GFAP may be included in specialized panels for traumatic brain injury (TBI), neuroinflammation, cognitive decline, long-COVID evaluation, autoimmune neurological disorders, and neurodegenerative disease research.
What does GFAP tell you?
GFAP reflects astrocyte activation or damage. Elevated levels may signal that the brain’s glial cells are responding to stress, inflammation, or tissue injury.
Low or undetectable GFAP levels are expected in healthy individuals.
Elevated GFAP
What does a high GFAP level mean?
An elevated GFAP level may indicate injury or inflammation in the central nervous system, including:
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Traumatic brain injury (TBI)
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Concussion or repeated head impacts
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Stroke or transient ischemic attack (TIA)
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Autoimmune encephalitis
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Multiple sclerosis (MS)
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Neurodegenerative disorders (e.g., Alzheimer's disease, Parkinson’s disease, ALS)
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Central nervous system infections (viral, bacterial, or autoimmune)
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Long-COVID–associated neuroinflammation (in emerging research)
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Brain tumor or astrocytoma (rare, but relevant in clinical evaluation)
Levels typically rise within hours after certain brain injuries and may remain elevated during active inflammation or neurodegeneration.
Symptoms that may accompany elevated GFAP
Symptoms vary depending on the cause but can include:
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Headache or persistent head pressure
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Memory changes or cognitive decline
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Confusion or difficulty concentrating (“brain fog”)
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Dizziness or imbalance
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Vision changes
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Tingling, numbness, or weakness
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Behavioral or personality changes
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Fatigue
If GFAP is elevated, clinicians usually evaluate other neurological markers and imaging studies before making a diagnosis.
Decreased or Normal GFAP
What does a low or normal GFAP mean?
Low or normal GFAP levels are typically normal and suggest that there is no active astrocyte injury or neuroinflammation detectable at the time of testing.
However, normal GFAP does not entirely rule out neurological disease. Timing, disease type, and severity influence levels, and some neurological conditions do not always elevate GFAP.
Factors that may affect GFAP levels
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Timing of injury or symptom onset
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Severity and type of neurological condition
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Blood-brain barrier integrity
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Age (levels tend to increase slightly with aging)
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Sample handling and laboratory methodology
What to do if your GFAP levels are high
Discuss results with your healthcare provider. They may consider:
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Neurological examination
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Follow-up testing with additional blood biomarkers (NFL, tau, UCH-L1, CRP, cytokines)
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MRI or CT imaging if clinically indicated
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Evaluation for autoimmune, infectious, or inflammatory causes
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Cognitive or neuropsychological testing if symptoms involve memory or cognition
Lifestyle and medical steps depend on the underlying cause. Early evaluation and intervention often support better outcomes.
Key Takeaway
GFAP is a specialized marker that reflects astrocyte health and central nervous system integrity. Elevated levels may signal brain injury or neuroinflammation, while low levels are typically normal. This test is most meaningful when interpreted in context—alongside symptoms, medical history, imaging, and other neurological markers.
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