Glial fibrillary acidic protein (GFAP) may serve as a serum marker of traumatic brain injury (TBI) that can be used to monitor biochemical changes in patients and gauge the response to treatment. 

Generally, GFAP can be reached at 4-6 hours after onset, and the peak is reached at 20 hours. And it lasts for few days or months.

Serum GFAP levels on admission and during the first 5 days of injury were increased in patients with severe TBI and were predictive of neurological outcome at 6 months.