The purpose of this study is to assess if putative brain injury biomarkers have utility as blood-based traumatic brain injury (TBI) diagnostic and monitoring tools. This will be accomplished by examining the relationships between potential serum-based TBI biomarkers and clinical measures of injury severity, occurrence of complications, and outcome, in subjects with mild or moderate TBI. The assay will be evaluated in a sample population of subjects over the age of 18 who have been referred to the health care provider for closed head injury evaluation.

Inclusion Criteria:

1. At least 18 years of age and no more than 80 years of age.
2. Closed injury to the head within 4 hours from symptom onset.
3. Glasgow Coma Scale (GCS) Score of 9-15.
4. Head Computerized Tomography (CT) performed as part of routine care.
5. Subject is willing to undergo the Informed Consent process prior to enrollment.
6. Based upon the Principal Investigator's opinion, subject is an appropriate candidate for the study.

Exclusion Criteria:

1. Participating in another clinical study that may affect the results of either study.
2. Time of injury cannot be determined.
3. Head CT not done as part of clinical emergency care.
4. Primary diagnosis of ischemic or hemorrhagic infarct.
5. Not available for 35 day follow-up visit.
6. Venipuncture not feasible.
7. Blood donation within 1 week of screening.
8. The Subject is otherwise determined by the Investigator to be medically unsuitable for participation in this study.

Subjects who present to the health care facility with Traumatic Brain Injury (GCS 9-15) within 4 hours of injury.