Diagnosing a traumatic brain injury (TBI) involves a combination of physical exams, cognitive testing, and imaging, with the specific tools depending on how severe the injury appears. There is no single test that confirms every TBI. Mild injuries like concussions can be especially tricky because they often don’t show up on standard brain scans, so clinicians rely on a layered approach that starts with bedside assessments and escalates to advanced imaging or blood tests when needed.
The First Assessment: Consciousness and Responsiveness
The Glasgow Coma Scale (GCS) is the starting point for nearly every suspected TBI. It scores three things: whether you can open your eyes, whether you can speak coherently, and whether you can move on command. Scores range from 3 to 15, with 15 being fully alert and oriented. A score of 13 to 15 indicates a mild brain injury, 9 to 12 is moderate, and 3 to 8 is severe. Emergency responders and ER doctors use the GCS within minutes of arrival to guide every decision that follows, from whether you need a CT scan to whether you need intensive care.
The GCS is quick and reliable, but it has limits. Someone with a concussion will almost always score 13 to 15, which tells clinicians the injury is in the mild range without revealing the full picture. That’s why additional tests are layered on top.
Physical and Neurological Exams
After scoring consciousness, clinicians check for specific physical signs that point to a more serious injury. These include repeated vomiting (two or more episodes), any sign of a skull fracture, clear fluid leaking from the nose or ears (which suggests a fracture at the base of the skull), bruising behind the ears, and whether the person is 65 or older. A dangerous mechanism of injury, like being hit by a car or falling from a significant height, also raises the level of concern. These criteria come from the Canadian CT Head Rule, a validated set of guidelines that helps clinicians decide who actually needs a CT scan and who can safely be observed.
A standard neurological exam also tests pupil reactions, reflexes, grip strength, sensation, and balance. Unequal pupil size or weakness on one side of the body can signal bleeding or swelling inside the skull that requires immediate intervention.
Eye Movement and Balance Testing
For suspected concussions and mild TBIs, a screening called VOMS (Vestibular/Ocular Motor Screening) has become a key diagnostic tool. It tests how well your eyes and balance system are working together, which is one of the functions most sensitive to brain injury.
During VOMS, a clinician asks you to track a finger smoothly from side to side, then up and down. Next, you rapidly shift your gaze between two fixed points, both horizontally and vertically. You’re also asked to slowly bring a small target toward your nose until you see double. A convergence point of 5 centimeters or more from the nose is considered abnormal. Finally, you focus on a stationary target while turning your head side to side or nodding up and down in time with a metronome.
After each test, you rate your headache, dizziness, nausea, and mental fogginess on a 0 to 10 scale. A spike in any of those symptoms during a specific test helps pinpoint which brain systems were affected, and it gives clinicians a measurable baseline to track your recovery over time.
Cognitive Testing
A concussion can impair memory, concentration, and processing speed even when a person looks physically fine. The Standardized Assessment of Concussion (SAC) is a brief test commonly used on sports sidelines and in emergency rooms. It evaluates four domains: orientation (knowing the date, time, and where you are), immediate memory (repeating back a list of words), concentration (reciting numbers backward or naming the months in reverse order), and delayed recall (remembering that word list after a few minutes).
Scores below expected thresholds suggest cognitive impairment consistent with a concussion. In sports settings, these results are most useful when compared against a baseline test taken before the season started, since “normal” cognitive performance varies widely from person to person.
CT Scans and When They’re Needed
A CT scan is the fastest way to check for skull fractures, bleeding inside the skull, and brain swelling. It’s the go-to imaging tool in emergency settings because it takes only minutes. However, not every head injury warrants one. The Canadian CT Head Rule identifies who needs scanning based on specific risk factors: failure to reach a GCS of 15 within two hours, suspected open skull fracture, signs of a fracture at the base of the skull, two or more episodes of vomiting, age 65 or older, amnesia extending more than 30 minutes before the injury, or a dangerous mechanism of injury.
If none of those criteria are present and the person is alert with a GCS of 15, observation alone is often appropriate. This matters because CT scans involve radiation exposure, and in mild injuries, the scan is overwhelmingly likely to come back normal.
MRI for Injuries CT Misses
CT scans are excellent at detecting bleeding and fractures but poor at revealing a common type of injury called diffuse axonal injury, where the brain’s internal wiring is damaged by rotational forces. This kind of damage is often invisible on CT.
MRI is far more sensitive. Specific MRI sequences are used depending on the type of damage suspected. FLAIR and diffusion-weighted imaging (DWI) are the most useful for detecting non-hemorrhagic damage to nerve fibers, while susceptibility-weighted imaging (SWI) picks up tiny hemorrhages scattered through the brain tissue. MRI is not typically done in the emergency room because it takes longer and requires the patient to lie still, but it becomes important when symptoms don’t match a normal-looking CT scan or when someone isn’t recovering as expected.
Blood Tests for Brain Injury
A blood test can now help determine whether a CT scan is necessary after a mild head injury. The FDA cleared the first TBI blood test in 2018, which measures two proteins that leak from damaged brain cells into the bloodstream. The test must be run on a blood sample collected within 12 hours of the suspected injury and is designed for adults 18 and older with a GCS of 13 to 15.
If the protein levels are below the cutoff, the chance of a significant finding on CT is very low, potentially sparing the patient from an unnecessary scan. If the levels are elevated, a CT scan is warranted. The blood test is not a standalone diagnostic tool. It’s used alongside the clinical picture to help guide imaging decisions, particularly in emergency departments seeing high volumes of head injuries.
Diagnosing TBI in Children
Children, especially those under two, present unique diagnostic challenges. They can’t describe their symptoms, and their skulls are thinner and more vulnerable. The PECARN criteria (developed from a large pediatric study) help clinicians decide which children need imaging while minimizing unnecessary radiation.
For children under two, a GCS of 15 with no altered mental status, no palpable skull fracture, no scalp swelling outside the forehead, no loss of consciousness lasting five seconds or more, no severe mechanism of injury, and parents reporting the child is acting normally places the child in a very low risk category where observation is usually sufficient. If any of those factors are present but the GCS is still 15 and mental status is normal, the child falls into an intermediate risk group where the decision to scan depends on clinical judgment and how the child looks over time. A GCS of 14, altered mental status, or a palpable skull fracture puts the child in the high-risk group where imaging is recommended.
When Symptoms Don’t Resolve
Most concussion symptoms clear up within two to six weeks. When they persist well beyond that window, the diagnosis shifts to post-concussion syndrome. There’s no single lab test or scan that confirms it. The diagnosis is based on the pattern: ongoing headaches, brain fog, dizziness, irritability, or sleep problems that trace back to a known head injury and haven’t resolved on a normal timeline. Clinicians commonly apply this label when symptoms last longer than three months, though some use six months or even a year as the threshold.
At this stage, the diagnostic approach often broadens to include detailed neuropsychological testing, which maps cognitive strengths and weaknesses across memory, attention, language, and problem-solving over the course of several hours. These results help distinguish post-concussion cognitive problems from other conditions like depression or anxiety, which can produce overlapping symptoms and sometimes develop alongside a brain injury.