Diagnosing a traumatic brain injury involves a combination of physical examination, standardized scoring systems, brain imaging, and sometimes blood tests or cognitive screening. There’s no single test that confirms every type of TBI. Instead, clinicians layer multiple assessments together, starting with a rapid severity check and then selecting further tools based on symptoms, the mechanism of injury, and how the person is responding in the moment.
The Glasgow Coma Scale: First Step in Severity
The Glasgow Coma Scale (GCS) is almost always the first diagnostic tool applied after a head injury. It scores three things: whether your eyes open on their own or only in response to pain or voice, whether your verbal responses make sense, and whether you can follow movement commands. The combined score falls on a scale from 3 to 15. A score of 14 or 15 is classified as mild TBI, 9 to 13 as moderate, and 3 to 8 as severe. This score shapes every decision that follows, from whether you need a CT scan to how urgently you’re triaged in an emergency department.
The GCS is quick, taking less than a minute, but it has limits. It can’t detect subtle cognitive problems, and it doesn’t capture the full picture in someone who appears alert but is confused or has memory gaps. That’s why it’s a starting point, not a final answer.
Neurological Exam at the Bedside
A neurological exam tests how well your brain is communicating with the rest of your body. It covers several areas in sequence. For mental status, you’ll be asked questions that check orientation (do you know where you are, what day it is) and short-term memory. Cranial nerve testing involves tracking eye movements, checking pupil reactions to light, testing facial muscle strength, and sometimes assessing hearing and sense of smell.
Movement and coordination checks include touching your nose with your eyes closed, walking in a straight line, and performing fine motor tasks like writing your name. Reflexes are tested by tapping your knee with a rubber hammer or stroking the sole of your foot to see how your nervous system responds automatically. A sensory exam might involve closing your eyes while the examiner moves your toes, places warm or cold objects on your skin, or brushes your skin with a cotton ball to see if you can detect it.
Each of these tests maps to a specific part of the nervous system. Abnormal results help pinpoint where the damage might be and how severe it is.
CT Scans: The First-Line Imaging Tool
A CT scan is the standard first imaging choice after head trauma. It’s fast, widely available, and excellent at detecting bleeding inside the skull, which is the most immediately dangerous complication. Over 75% of acute head trauma cases are classified as mild, and of those, over 75% have a normal GCS score of 15. Because of this, clinical guidelines recommend selective scanning rather than imaging everyone. The decision to order a CT is based on specific risk factors rather than the head injury alone.
Not everyone with a head injury needs a CT. Clinical decision rules help doctors determine who does. For adults, red flags include loss of consciousness, vomiting, worsening headache, signs of a skull fracture, confusion, or a dangerous mechanism of injury (such as being hit by a car or falling from a height). If none of these are present, observation alone may be appropriate.
CT does have a significant blind spot: it often misses subtle brain injuries like diffuse axonal injury, which happens when the brain’s nerve fibers are stretched and torn by rotational forces. This type of damage can cause real symptoms even when the CT looks completely normal.
When MRI Becomes Necessary
MRI comes into play when someone has persistent neurological symptoms that a CT scan can’t explain. It offers far better contrast resolution for soft tissue, making it capable of detecting microbleeds, diffuse axonal injury, and other damage that CT simply cannot see. Advanced MRI techniques can reveal injuries invisible on standard imaging, which is particularly valuable in the days and weeks after the initial trauma.
The American College of Radiology recommends MRI especially in subacute or chronic phases, when symptoms linger but the initial CT was normal. If there’s concern about blood vessel damage, CT angiography may also be ordered. If a cerebrospinal fluid leak is suspected, thin-section CT imaging of the skull base is the preferred study.
Blood Tests for Brain Injury
In 2018, the FDA cleared the first blood test for TBI, called the Brain Trauma Indicator. It measures two proteins that leak from damaged brain cells into the bloodstream: one released from structural support cells in the brain and another from neurons themselves. When these protein levels are low, it’s a strong signal that no bleeding is present inside the skull, potentially allowing patients with mild TBI to skip a CT scan and its radiation exposure.
The test works best when blood is drawn within about two hours of injury. It’s designed specifically for mild TBI and helps answer one question: is a CT scan needed? It doesn’t diagnose the full extent of brain injury or predict long-term outcomes.
Concussion-Specific Assessment Tools
For sports-related injuries and milder head trauma, the Sport Concussion Assessment Tool (now in its sixth version, SCAT6) provides a structured evaluation. It combines several components into one standardized checklist: a graded symptom checklist, the GCS, questions that test orientation and immediate memory, balance testing, a neurological screen, and a reading ability measure. It also includes observational signs that a trained evaluator watches for during testing.
The SCAT6 is most valuable when a baseline test exists for comparison. Many sports programs have athletes complete a pre-season assessment so that post-injury scores can be measured against their personal normal. Without a baseline, the tool still helps, but interpreting borderline results becomes harder.
Computerized Cognitive Testing
Tools like the ImPACT test measure specific brain functions through a computer-based battery. The test generates scores across five areas: verbal memory, visual memory, reaction time, processing speed, and impulse control. These scores can reveal deficits that aren’t obvious during a standard neurological exam.
There are gaps, though. Two cognitive abilities commonly affected by mild TBI, sustained attention and auditory working memory, are not directly captured by the ImPACT battery. Processing speed, visual memory, and impulse control have been identified as the most useful scores for distinguishing concussed individuals from healthy ones. Like the SCAT, these tests are most powerful when compared against a pre-injury baseline.
Diagnosing TBI in Children
Children present a unique challenge because CT scans carry a proportionally higher radiation risk, and young children can’t always describe their symptoms. The PECARN clinical decision rule is the most widely validated tool for deciding whether a child needs a head CT after injury. It uses different criteria depending on age.
For children under 2, the rule looks at mental status, whether the child is behaving normally per the caregiver, loss of consciousness, the severity of the injury mechanism, the location of any scalp swelling (non-frontal hematomas are more concerning), and signs of skull fracture. For children aged 2 to 15, the criteria shift to include vomiting, severe headache, and signs of a basilar skull fracture. If all the low-risk criteria are met, the child is very unlikely to have a significant brain injury, and observation without a CT is generally appropriate.
When Symptoms Don’t Resolve
Most concussion symptoms clear within 30 days. When they persist beyond three months, the condition is classified as persistent post-concussive syndrome. Diagnosis requires cognitive deficits in attention or memory plus at least three of the following: fatigue, sleep disturbance, headache, dizziness, irritability, mood changes, or personality changes. These symptoms must represent a change from how the person functioned before the injury.
This diagnosis is largely clinical, meaning it relies on symptom reporting and cognitive testing rather than imaging. MRI and CT are often normal in these cases, which can be frustrating for patients who feel genuinely impaired but are told their scans look fine. Neuropsychological testing, a more detailed version of cognitive screening that can take several hours, is often the most revealing diagnostic tool at this stage. It maps strengths and weaknesses across memory, attention, language, and executive function in enough detail to guide rehabilitation.