The study is intended to cover two purposes: first, to develop a blood-based biomarker test for aiding the diagnosis of traumatic brain injury (TBI) in adult participants and for prognosis of outcome of TBI (CLIN12.1); and second, for monitoring the development of secondary events in adult participants diagnosed with TBI (CLIN12.2).

Inclusion Criteria:

• Presenting to the Emergency Department with a biomechanically plausible mechanism of non-penetrating traumatic brain injury (TBI; direct impact: blow to the head, head against object, object against head; acceleration/deceleration)
• Acute brain CT completed for standard of care

Further Inclusion Criteria (specific for CLIN12.2):

• Admitted to the hospital with radiographic evidence of acute TBI
• Admitted to the intensive care unit at risk for decline related to TBI

Exclusion Criteria:

• Prior neurosurgical intervention within the last 6 months
• Major debilitating neurological disease (such as, but not limited to: stroke, CVA, mild cognitive impairment, Alzheimer's disease, Amyotrophic lateral sclerosis, Parkinson's disease, Huntington's disease, Frontotemporal dementia, tumor, epilepsy, unmanaged seizure disorder), impairing baseline awareness, cognition, or validity of outcomes assessments
• Major debilitating baseline mental health disorders (such as but not limited to schizophrenia or bipolar disorder) that would interfere with follow-up and the validity of outcome assessments
• Significant pre-existing conditions that would interfere with follow-up and outcome assessment (such as, but not limited to: chronic kidney disease, chronic cardiovascular comorbidities, alcohol or substance use disorder)
• History of melanoma
• Primary diagnosis of ischemic or hemorrhagic stroke
• Any spinal Cord Injury (American Spinal Injury Association [ASIA] score of A-D)
• Received chemotherapy or radiation currently or within the last year
• Patients on psychiatric hold (e.g., 5150, 5250)
• Current incarceration or in custody
• Known inability to undergo an MRI
• Currently receiving any interventional treatments as a part of an investigational study/trial (drug, device, behavioral, treatment) at the time of enrollment and/or during the course of this study
• Low likelihood of follow-up (e.g. participant or family indicating low interest, residence in another state or country, homelessness or lack of reliable contacts)
• Any condition that, in the opinion of the investigator, could interfere in the proper execution of the study procedures and/or in their future permanence in the study

Participants who present at the emergency department with suspected TBI as per the eligibility criteria from approximately 10 to 15 sites in geographically diverse locations within the United States.