Concussion is diagnosed clinically, meaning no single blood test, brain scan, or gadget can confirm it on its own. A clinician pieces the picture together from your symptoms, your account of what happened, a focused neurological exam, and a battery of functional tests covering memory, balance, and eye movements. The challenge is that concussion symptoms overlap heavily with other conditions, standard imaging usually looks normal, and the tools available each have real blind spots. Understanding which tests matter, what they can and cannot tell you, and which warning signs demand urgent attention puts you in a better position to get the right care at the right time.
Red Flags That Require Emergency Evaluation
Before worrying about formal concussion testing, the first priority after a head injury is ruling out something more dangerous, like bleeding inside the skull. Emergency departments follow a structured approach: identify the injury mechanism, document symptoms, and screen for red flags that suggest a more severe brain injury needing immediate intervention.1Handbook of Clinical Neurology. Emergency department evaluation of the concussed athlete Several warning signs carry high sensitivity for serious intracranial problems:
- Loss of consciousness: especially if prolonged or worsening
- Repeated vomiting: more than a single episode
- Seizure: any convulsive activity after the impact
- Severe or worsening headache: one that escalates rather than stabilizing
- Increasing confusion or agitation: inability to recognize people or places
- Weakness or numbness on one side of the body
- Slurred speech or inability to be awakened
These red flags appear on the Sport Concussion Assessment Tool (SCAT) and overlap with criteria used in emergency clinical decision rules.2PubMed. Evolving the SCAT5 for Ruling Out Higher-Severity Traumatic Brain Injuries-Can Decision Rules Developed for Emergency Settings Help? If any of them are present, go to an emergency department. The rest of this article covers what happens when those red flags are absent and the question shifts from “is this an emergency?” to “is this a concussion, and how bad is it?”
The Sideline Assessment
In sports settings, the most widely used tool is the Sport Concussion Assessment Tool, now in its sixth version (SCAT6). It is designed for healthcare professionals to administer to athletes aged thirteen and older and covers multiple domains in a single structured evaluation: level of consciousness, orientation questions, a symptom checklist, cognitive screening (things like word recall and number sequences), a neck exam, balance testing, and coordination tasks.3PubMed Central. Sport concussion assessment tool™ – 6 (SCAT6) The tool’s value is that it forces the examiner to check each domain rather than relying on a gut feeling. An athlete who “feels fine” but stumbles through the balance component or cannot recall a five-word list has objective evidence of impairment.
One limitation worth knowing: the SCAT6 is meant for trained clinicians, not coaches or parents. A simplified version exists for non-medical personnel (the Concussion Recognition Tool), but it is designed only to flag whether someone needs professional evaluation, not to diagnose anything. Another limitation is that sideline tools work best when a pre-season baseline score exists for comparison, and baseline scores come with their own complications, discussed below.
Eye Movements and Vestibular Screening
One of the most sensitive clinical tools for concussion is the Vestibular/Ocular Motor Screening, or VOMS. It checks how well you can track objects with your eyes, shift your gaze rapidly between two targets, and maintain visual focus during head movement. After each task, the examiner asks whether your symptoms (headache, dizziness, nausea, fogginess) have increased. A concussed brain frequently struggles with these tasks even when everything else looks passable.
In a large study from the NCAA-Department of Defense concussion research consortium, the VOMS overall score distinguished concussed collegiate athletes from healthy controls with high accuracy.4PubMed. Discriminative Validity of Vestibular Ocular Motor Screening in Identifying Concussion Among Collegiate Athletes An earlier study found the VOMS had very high sensitivity at about 96%, though specificity was lower, meaning it is better at catching concussions than at ruling them out in people who are symptomatic for other reasons.5The Journal of Head Trauma Rehabilitation. Clinical Detection and Recovery of Vestibular and Oculomotor Impairments Among Amateur Athletes Following Sport-Related Concussion The test takes about five minutes and requires no equipment beyond a target to track, making it practical in a clinic or even on the sideline with a trained examiner.6PubMed Central. A Brief Vestibular/Ocular Motor Screening (VOMS) assessment to evaluate concussions
Balance Testing and Its Quirks
The Balance Error Scoring System (BESS) has been a staple of concussion evaluation for years. You stand in three stances (feet together, single leg, heel-to-toe) on both a firm surface and a foam pad, eyes closed, while an examiner counts your errors: wobbling, lifting your hands off your hips, opening your eyes, stepping out of position. A total error score above roughly 21 has been used as a threshold to flag possible concussion in some studies, with about 60% sensitivity and 82% specificity in adolescents.7PubMed Central. Comparison of the balance accelerometer measure and balance error scoring system in adolescent concussions in sports
The BESS has a well-documented problem, though: a practice effect. People who take the test repeatedly get better at it simply through familiarity. In one study of college-aged adults, the improvement from practice did not disappear even after four weeks, and more than a fifth of participants showed improvement that exceeded the test’s minimum detectable change threshold. That means an athlete who has memorized the feel of the test could score “normal” after a concussion because their baseline was artificially inflated by practice sessions.8PubMed Central. The Balance Error Scoring System Learned Response Among Young Adults Adding an inertial sensor to the standard BESS improves its diagnostic accuracy by picking up subtle sway patterns the human eye misses, which could help close this gap.9PubMed Central. Instrumenting the Balance Error Scoring System for use with patients reporting persistent balance problems after mild traumatic brain injury
Computerized Neurocognitive Tests
Programs like ImPACT, Axon (formerly CogSport), and ANAM are computerized batteries that measure reaction time, memory, processing speed, and attention. They are widely used in collegiate and professional sports, and many high schools now require athletes to complete a baseline test before the season. The idea is straightforward: if you perform worse than your own baseline after a head hit, something has changed.
The reality is messier. A large consortium study found that ImPACT’s sensitivity for detecting concussion was only about 58 to 63%, and specificity hovered in a similar range. The other two major tests performed comparably or worse.10PubMed. Sensitivity and Specificity of Computer-Based Neurocognitive Tests in Sport-Related Concussion A head-to-head comparison found that the sensitivity of reliable change scores was strongest in the first 24 hours after injury and dropped off quickly afterward.11Journal of the International Neuropsychological Society. Prospective, Head-to-Head Study of Three Computerized Neurocognitive Assessment Tools (CNTs) Broader reviews have noted support for some aspects of validity but persistent questions about clinical usefulness, particularly beyond the acute injury window.12PubMed Central. A review of the validity of computerized neurocognitive assessment tools in mild traumatic brain injury assessment
None of these tests should be used as the sole basis for a concussion diagnosis. They are one piece of a multi-dimensional evaluation. Using them alone would miss a meaningful number of concussions and also flag some healthy people.
The Sandbagging Problem
Baseline testing has an obvious vulnerability: an athlete who deliberately performs poorly at baseline creates a low bar that is easy to clear after an actual injury. Research on this is somewhat reassuring. In one study, participants who were instructed to fake a bad baseline on ImPACT while avoiding detection mostly got caught by the test’s built-in validity indicators. Only about one in ten succeeded.13PubMed. Neuropsychological testing for sports-related concussion: how athletes can sandbag their baseline testing without detection A similar study on CNS Vital Signs found a higher rate of undetected sandbagging, around a third, suggesting the problem varies by platform.14PubMed. The ability of CNS vital signs to detect coached sandbagging performance during concussion baseline testing Supervised, well-proctored test sessions reduce the risk, but clinicians should never rely on a single baseline comparison to clear an athlete.
When a CT Scan Is and Is Not Helpful
A CT scan after a head injury is looking for one thing: bleeding or structural damage inside the skull. It is not looking for concussion itself. The vast majority of concussions produce a completely normal CT, and a normal result does not mean the brain is uninjured.15PubMed. Bench to bedside: evidence for brain injury after concussion–looking beyond the computed tomography scan The scan is still critical when red flags are present because it catches bleeds and skull fractures that require surgical intervention.
Emergency physicians use validated clinical decision rules to determine who needs a CT and who can safely skip one. The Canadian CT Head Rule is the best-studied example. A meta-analysis found it catches over 90% of clinically important brain injuries while sparing a meaningful proportion of patients from unnecessary radiation, though its specificity is modest, meaning it still sends plenty of people who turn out to be fine to the scanner.16PubMed Central. Accuracy of Canadian CT Head Rule and New Orleans Criteria for Minor Head Trauma; a Systematic Review and Meta-Analysis A large implementation trial of the rule found no missed brain injuries or adverse outcomes, which is the goal: it is designed to be cautious.17PubMed Central. A prospective cluster-randomized trial to implement the Canadian CT Head Rule in emergency departments
Blood Biomarkers
The FDA cleared a blood test in 2018 that measures two proteins (GFAP and UCH-L1) released into the bloodstream when brain cells are damaged. Its clinical role is narrow but valuable: it helps emergency physicians decide whether a patient with mild traumatic brain injury needs a CT scan. A recent study of a high-performance version of this test found it had roughly 97% sensitivity and a very high negative predictive value, above 99%, meaning that a negative result makes intracranial injury extremely unlikely.18PubMed. A high-performance core laboratory GFAP/UCH-L1 test for the prediction of intracranial injury after mild traumatic brain injury The trade-off is low specificity, around 40%, so a positive result does not confirm a bleed; it just means a CT scan is warranted. The test is a triage tool for imaging decisions, not a concussion diagnosis in itself.
Research on salivary biomarkers is further from clinical use but intriguing. Small molecules called microRNAs found in saliva appear to differ between concussed and non-concussed individuals. In one pediatric study, a panel of five salivary microRNAs identified children who would go on to have prolonged symptoms more accurately than the standard symptom checklist.19JAMA Pediatrics. Association of Salivary MicroRNA Changes With Prolonged Concussion Symptoms Other research has found that salivary microRNA profiles differ over time in children who develop persistent symptoms compared to those who recover quickly.20Frontiers in Public Health. Salivary miRNA Expression in Children With Persistent Post-concussive Symptoms These remain research tools, not something your doctor can order today, but they point toward a future where a spit test helps predict recovery trajectory.
Advanced Brain Imaging
If standard CT and MRI miss concussion-related damage, more advanced imaging techniques can detect subtler changes, at least at the group level. Diffusion tensor imaging (DTI) measures the movement of water molecules along the brain’s white matter tracts and can reveal microstructural disruption invisible on conventional scans. Studies of concussed athletes have found changes in white matter within 48 hours of injury, particularly in frontal brain regions.21PubMed Central. Acute White-Matter Abnormalities in Sports-Related Concussion Some of these white matter changes persist even after athletes have been medically cleared to return to play.22PubMed Central. White matter during concussion recovery: Comparing diffusion tensor imaging (DTI) and neurite orientation dispersion and density imaging (NODDI)
The catch is that DTI reliably detects differences between concussed and healthy groups in research, but it does not yet work well enough for diagnosing an individual patient. A systematic review concluded there is insufficient evidence that DTI can serve as a diagnostic tool at the individual level despite twenty years of refinement.23PubMed Central. Diffusion Tensor Imaging of TBI: Potentials and Challenges Similarly, quantitative EEG (qEEG), which uses computer analysis to detect abnormal brainwave patterns, can identify changes in brain function after injury, including increases in slow-wave activity and reduced connectivity between brain regions.24PubMed. Quantitative Electroencephalography Objectivity and Reliability in the Diagnosis and Management of Traumatic Brain Injury But like DTI, qEEG is not yet part of routine clinical concussion diagnosis.25PubMed Central. The Role of Quantitative EEG in the Diagnosis of Neuropsychiatric Disorders These technologies are useful in research and may eventually sharpen individual-level diagnosis, but today they supplement rather than replace the clinical exam.
The Whiplash Overlap
One of the trickiest aspects of concussion diagnosis is distinguishing it from a cervical spine (neck) injury. Whiplash and concussion share a startling number of symptoms: headache, dizziness, difficulty concentrating, fatigue, irritability, and sensitivity to light or noise. A systematic review found the two conditions overlap in symptoms, biomechanics, and even some imaging findings, while differing mainly in postural patterns and the type of vestibular problems they produce.26PubMed. How similar are whiplash and mild traumatic brain injury? A systematic review The clinical presentations are so similar that symptoms alone cannot distinguish a brain injury from a cervical or vestibular injury after a head impact.27Clinical Journal of Sport Medicine. Brain or Strain? Symptoms Alone Do Not Distinguish Physiologic Concussion From Cervical/Vestibular Injury
This matters because the treatment pathways differ. Neck-driven symptoms respond to manual therapy, vestibular rehabilitation, and targeted exercise. Concussion-driven symptoms have their own rehabilitation protocols. The practical takeaway is that a thorough concussion evaluation should include a cervical spine exam and vestibular/ocular testing, not just cognitive screening.28PubMed. Whiplash Injury or Concussion? A Possible Biomechanical Explanation for Concussion Symptoms in Some Individuals Following a Rear-End Collision If you are diagnosed with a concussion but your symptoms are not improving with standard management, it is worth asking whether a neck injury might be part of the picture.
Special Populations and Complicating Factors
Children
Young children present a particular diagnostic challenge. There are no validated sideline assessment tools for children under thirteen, and no single pediatric concussion tool has been validated from sideline through all stages of recovery.29PubMed. The evaluation and management of acute concussion differs in young children Young children may not be able to describe symptoms like fogginess or feeling “off,” so clinicians lean more heavily on observed behavior changes: increased irritability, altered sleep, reluctance to play, and changes in eating patterns. Parents become essential informants in a way they are not for older athletes.
Sex Differences
Whether males and females experience concussion differently is a question researchers keep circling. A meta-analysis found that at baseline, females report higher rates of several symptoms including headache, difficulty concentrating, and sleep disturbances, which means the same post-concussion symptom checklist score might mean different things depending on sex.30PubMed. Differences in Symptom Reporting Between Males and Females at Baseline and After a Sports-Related Concussion After concussion, the actual symptom differences were small and clinically insignificant, with the one exception that females were less likely to report confusion. A broader review concluded that findings remain mixed on whether sex affects brain structure changes, functional imaging results, or recovery timelines after concussion.31PubMed Central. Sex-Related Differences in the Effects of Sports-Related Concussion The practical implication is that sex-specific baseline norms matter, but there is no clear evidence that the diagnostic process itself should differ.
ADHD and Learning Disabilities
Pre-existing attention deficit hyperactivity disorder or learning disabilities can significantly muddy neurocognitive test results. A study from the NCAA-DoD CARE Consortium found that in athletes with ADHD or learning disabilities, the ImPACT test’s sensitivity and specificity both fell below levels considered clinically useful across every analytical method tested.32PubMed. Sensitivity and Specificity of the ImPACT Neurocognitive Test in Collegiate Athletes and US Military Service Academy Cadets with ADHD and/or LD This does not mean people with ADHD cannot be tested for concussion. It means clinicians working with this population should rely even more heavily on the multi-tool approach rather than leaning on a single computerized test.
Exercise Tolerance Testing
The Buffalo Concussion Treadmill Test (BCTT) takes a different approach to concussion assessment. Instead of testing what the brain can do while you sit still, it measures how the brain handles the cardiovascular stress of exercise. You walk or jog on a treadmill at gradually increasing intensity while a clinician monitors your heart rate and symptoms. A concussed brain often cannot tolerate the cardiovascular demands that a healthy brain handles easily, and the test looks for the point at which concussion symptoms flare up or the heart rate response becomes abnormal.
In adolescents, a gap of 50 beats per minute or less between resting and peak exercise heart rate on the BCTT was about 73% sensitive and 78% specific for predicting prolonged recovery.33Frontiers in Neurology. The Predictive Capacity of the Buffalo Concussion Treadmill Test After Sport-Related Concussion in Adolescents A newer study in adults suggests that the inability to reach 90% of your age-predicted maximum heart rate is a useful marker of autonomic dysfunction after mild traumatic brain injury, though the researchers caution that physical fitness levels can confound the results.34PubMed. Performance and Physiological Response to the Buffalo Concussion Treadmill Test Can Identify Autonomic Dysfunction in the General Adult Population With Mild Traumatic Brain Injury The BCTT is increasingly used both as a diagnostic aid and as a guide for prescribing graded exercise during recovery.
When Symptoms Persist
Most concussion symptoms resolve within two to four weeks, but a subset of people develop persistent symptoms lasting months or longer. Diagnosing this condition is surprisingly contentious. Two major diagnostic systems have used different criteria for it, and the stricter set (from the DSM-IV) identified only about 11% of patients at three months, while the broader set (from the ICD-10) captured 64% of the same group.35PubMed. Diagnostic criteria for postconcussional syndrome after mild to moderate traumatic brain injury Even more problematic, the symptoms that define persistent post-concussion syndrome are common in people who never hit their heads at all. One study found that people with non-head injuries met ICD-10 criteria for post-concussion syndrome at essentially the same rate as those with actual mild traumatic brain injuries.36PubMed. Post-concussion syndrome: prevalence after mild traumatic brain injury in comparison with a sample without head injury
In children and adolescents, this diagnostic fuzziness is compounded by life circumstances. A study examining definitions of persistent symptoms in youth found that factors like poor sleep the night before testing or current psychological distress dramatically inflated symptom scores. Among girls experiencing even mild psychological distress, about 40% met one common definition for persistent post-concussion symptoms, compared to only 2% of girls without pre-existing issues or current distress.37Frontiers in Neurology. Examining Criteria for Defining Persistent Post-concussion Symptoms in Children and Adolescents This does not mean persistent symptoms are imagined. It means that diagnosing them requires careful attention to context, including sleep, mental health, and life stressors, rather than simply counting symptoms on a checklist.
Why No Single Test Is Enough
Every diagnostic tool described here has a gap. Computerized cognitive tests miss too many concussions to stand alone. Balance tests have practice effects. Eye-movement screening is sensitive but can flag non-concussion vestibular issues. CT scans only catch bleeding. Blood biomarkers triage for imaging, not for concussion itself. Advanced imaging works at the group level but not for your individual brain. The consistent finding across the concussion research literature is that multi-dimensional assessment outperforms any single tool.
What that means for you in practice: if you or someone you know has taken a blow to the head and something feels off, the right evaluation involves a clinician who checks symptoms, cognition, balance, eye function, and neck integrity as a package. A doctor who bases a concussion diagnosis or clearance decision on one computerized test score is not following the evidence. And if symptoms linger past a few weeks, the evaluation should expand to consider exercise tolerance, psychological contributors, and whether neck injury is part of the problem rather than just repeating the same symptom checklist.