The present disclosure relates to methods for diagnosing and evaluating a subject that has sustained or may have sustained an injury to the head, such as a traumatic brain injury (TBI). In particular, the present disclosure identifies various biomarkers, the detection and/or differential expression of which can be used to assess the presence or absence of a TBI in a subject, and can be used as a basis for diagnosing a subject as having a specific type of TBI (e.g., severe TBI or subclasses of mild TBI). The various TBI biomarkers can be detected individually or in combination and can be used as an important diagnostic, prognostic, and/or TBI risk stratification tool as part of assessing a subject's TBI status.