Traumatic Brain Injury Biomarker Panel

The i-STAT TBI test is a panel of in vitro diagnostic immunoassays for the quantitative measurements of glial fibrillary acidic protein (GFAP) and ubiquitin carboxyl-terminal hydrolase L1 (UCH-L1) in whole blood and a semi-quantitative interpretation of test results using the i-STAT Alinity instrument. The interpretation of test results is used, in conjunction with other clinical information, to aid in the evaluation of patients, 18 years of age or older, presenting with suspected mild traumatic brain injury (Glasgow Coma Scale score 13-15), which may include one of the following four clinical criteria: 1) any period of loss of consciousness, 2) any loss of memory for events immediately before and after the accident, 3) any alteration in mental state at the time of accident, and/or 4) focal neurological deficits, within 24 hours of injury, to assist in determining the need for a CT (computed tomography) scan of the head.

Traumatic brain injury (TBI) is the structural injury or physiologic disruption of brain function caused by the impact of an external mechanical force on the brain. The resulting injury can be ranked from mild to severe based on clinical symptoms, level of consciousness, and neuroimaging techniques; such as Magnetic Resonance Imaging (MRI) and Computed Tomography (CT) scan. While severe TBI presents with more overt symptoms, patients presenting with mild TBI remain difficult to diagnose objectively and may necessitate the use of neuroimaging techniques in the acute assessment of head injuries. However, an estimated 90% of head CT scans in patients suspected of having mild TBI have negative results for clinically important brain injuries which unnecessarily expose the patients to a dose of radiation comparable to eight months of background radiation. 

Measurement of glial fibrillary acid protein (GFAP) and ubiquitin carboxyl-terminal hydrolase L1 (UCH-L1) released from the brain into the blood has been proposed as a method of preventing unnecessary use of neuroimaging, and reducing associated radiation exposure in patients suspected of having mild TBI.

Glial Fibrillary Acidic Protein

Glial fibrillary acidic protein (GFAP) is an astrocyte structural protein which is found in brain parenchyma. GFAP is increased in TBI patients with an abnormal CT and is elevated in patients with axonal injury three months post injury. GFAP is detectable in serum less than 1 hour after head injury and distinguishes between trauma patients with mild TBI and those without head injury. It is also elevated in patients with traumatic intracranial abnormalities on CT compared with those without lesions and could also be used to predict those patients who required neurosurgical intervention.

Ubiquitin Carboxyl-Terminal Hydrolase L1

Ubiquitin carboxyl-terminal hydrolase-L1 (UCH-L1) is a protein that is involved in the metabolism of ubiquitin within neurons. Increases in blood UCH-L1 have been detected in the serum of mild and moderate TBI patients within an hour of injury. Levels measured within 4 hours of injury were significantly higher in those with TBI lesions on CT than those with a normal intracranial appearance on CT. Blood levels of UCH-L1 have been demonstrated to be able to discriminate mild TBI patients from patients without head injuries and, similar to GFAP, UCH-L1 levels were much higher in patients who required neurosurgical intervention.