An excellent review of diagnostic issues related to mild traumatic brain injury (mTBI) and post-concussion syndrome (PCS) can be found in McCrea (2008). He clearly breaks down the various diagnostic systems that are currently used for head injuries.
The American Congress of Rehabilitation Medicine (ACRM) developed one of the most accepted diagnostic criteria for mild traumatic brain injury (mTBI). The criterion states that a person must have experienced a traumatically induced disruption of brain function manifested by at least one of the following: 1. Any period of loss of consciousness 2. Any loss of memory for events immediately before or after the accident 3. Any alteration in mental state at the time of the accident, for example, being dazed, disoriented, or confused 4. Focal neurological deficits that may or may not be transient.