1. A method of determining the presence of traumatic brain injury (TBI) in a subject, comprising: measuring the amount of neurensin (p24) in a sample of cerebral spinal fluid (CSF) or blood from a subject at a time within and up to about 84 hours following occurrence of a suspected TBI; and comparing the amount of p24 in said sample with the amount of p24 in a respective s ample from an uninjured subject; wherein a higher amount of p24 in the subject sample relative to the amount in a CSF or blood sample from the uninjured subject is indicative of TBI in the subject suspected of having the TBI.