Disclosed herein are methods and systems of determining whether a subject’s levels of GFAP, UCH-L1, or GFAP and UCH-L1 are elevated in a sample collected from the subject. The methods comprise determining whether the levels of GFAP, UCH-L1, or GFAP and UCH-L1 are elevated in the sample, and communicating the determination on or from an instrument. The methods may be used to aid in the diagnosis and evaluation of a subject (e.g., a human subject) that has sustained or may have sustained an injury to the head, such as to determine whether the subject is suffering from a mild, moderate, severe, or moderate to severe traumatic brain injury (TBI).