Concussions are diagnosed primarily through a combination of symptom evaluation, physical examination, and cognitive testing rather than a single definitive test. No blood test or brain scan can confirm a concussion on its own. Standard imaging like CT scans and MRIs appear normal in concussion patients, which means diagnosis relies on a clinician’s assessment of how you feel, how you think, and how your body responds to specific physical challenges.
Why Imaging Doesn’t Show a Concussion
This surprises many people, but a concussion won’t show up on a standard CT scan or MRI. These scans reveal structural damage like bleeding or skull fractures, not the cellular-level disruption that causes concussion symptoms. That’s actually an important distinction: if imaging does show something abnormal, the injury is more severe than a typical concussion.
Doctors use CT scans not to confirm a concussion but to rule out more dangerous injuries like brain bleeds. A set of criteria known as the Canadian CT Head Rule helps clinicians decide who actually needs a scan. Five high-risk factors trigger the recommendation: not returning to full alertness within two hours, a suspected open skull fracture, signs of a fracture at the base of the skull, vomiting two or more times, or being 65 years or older. Two additional factors, including memory loss of more than 30 minutes before the injury and a dangerous mechanism of injury (like being hit by a car or falling from a height), also raise the threshold for scanning. Using these criteria, only about a third to half of head injury patients need a CT at all.
A newer option is a blood test cleared by the FDA for adults 18 and older. Abbott’s rapid bedside test measures two proteins that brain cells release into the bloodstream after injury. Results come back in about 15 minutes and can be used up to 24 hours after the injury. The test helps clinicians decide whether a CT scan is necessary, potentially sparing patients from unnecessary radiation. It does not diagnose concussion itself.
What Clinicians Look for First
The initial evaluation focuses on observable signs and a few quick questions. If someone takes a blow to the head during a game, at work, or in an accident, certain signs point strongly toward concussion: lying motionless after impact, falling without bracing, stumbling or showing obvious coordination problems, appearing confused or staring blankly, or having a seizure. Any of these warrants immediate evaluation.
A quick memory check can also be revealing. In sports settings, clinicians ask questions like “What venue are we at today?” or “Who scored last?” These aren’t trick questions. They test whether the brain is processing and storing information normally in real time. Getting any of them wrong, or being slow and uncertain, signals the need for a more thorough assessment.
The Symptom Checklist
The most widely used concussion assessment tool, now in its sixth edition (SCAT6), includes a 22-item symptom checklist. You rate each symptom on a severity scale. The list covers the full range of what concussion can do to you:
- Physical: headache, pressure in the head, neck pain, nausea or vomiting, dizziness, blurred vision, balance problems, sensitivity to light, sensitivity to noise, fatigue
- Cognitive: feeling slowed down, feeling “in a fog,” difficulty concentrating, difficulty remembering, confusion, drowsiness
- Emotional: feeling more emotional than usual, irritability, sadness, nervousness or anxiety
- Sleep: trouble falling asleep
Not everyone gets the same symptoms. Some people have a pounding headache and nausea. Others feel mentally foggy with no headache at all. The pattern and severity help clinicians gauge the injury and track recovery over time. One important detail: about 17% of concussion patients, particularly in younger athletes, don’t notice symptoms right away. In those with delayed onset, the median time to first symptoms is about 60 minutes, though it can take hours. This is why someone who “feels fine” immediately after a head impact still needs monitoring.
Cognitive and Memory Testing
A concussion often disrupts thinking before you’re fully aware of it. The cognitive portion of the assessment tests orientation, memory, and concentration in structured ways.
For orientation, you’ll be asked the month, date, day of the week, year, and current time (within one hour). These seem simple, but a concussed brain can stumble on them. For memory, you’ll hear a list of 10 words read aloud three times and try to recall as many as possible after each reading, then again after a delay. Concentration is tested by reciting digits backward and listing the months of the year in reverse order. Poor performance on any of these, especially compared to a baseline test taken before injury, is a strong diagnostic signal.
Balance and Coordination Tests
Concussions frequently affect balance, even when people don’t realize it. The modified Balance Error Scoring System (mBESS) has you stand in three positions with your eyes closed: feet together, one foot in front of the other (tandem stance), and on one leg. A clinician counts how many times you sway, stumble, or open your eyes. Timed tandem gait testing adds a walking component: you walk heel-to-toe along a line as quickly as possible, turn, and come back. An optional version adds a mental task, like counting backward by sevens while walking, to see how your brain handles two demands at once.
Eye and Vestibular Screening
One of the most sensitive ways to detect concussion involves testing how your eyes and inner ear system work together. The Vestibular/Ocular Motor Screening (VOMS) puts your visual and balance systems under specific stress, then asks you to rate any headache, dizziness, nausea, or fogginess on a 0-to-10 scale after each task.
The screen includes several components. Smooth pursuits test whether your eyes can smoothly follow a moving target side to side and up and down. Saccades test whether you can snap your gaze quickly between two fixed points. Near point convergence checks whether both eyes can track an object as it moves toward your nose. Normally, your eyes stay locked on the target until it’s within a few centimeters. A convergence point of 5 centimeters or more from your nose is considered abnormal and is a common finding after concussion.
The vestibular-ocular reflex test has you focus on a stationary target while turning your head side to side or up and down at a set pace. If your eyes can’t stay locked on the target, or if the movement triggers symptoms, it suggests the brain’s ability to coordinate head movement with vision has been disrupted. These tests are particularly useful because they can detect problems that a basic symptom checklist might miss.
Danger Signs That Need Emergency Care
Most concussions don’t require emergency imaging or hospitalization, but certain symptoms after a head injury signal something more serious. The CDC identifies these as danger signs that warrant calling 911 or going to the emergency department:
- Seizures or visible shaking and twitching
- Not recognizing familiar people or places
- Repeated vomiting
- Increasing confusion, agitation, or unusual behavior
- Growing drowsiness or inability to stay awake
- Slurred speech, weakness, numbness, or worsening coordination
- A headache that keeps getting worse
- One pupil noticeably larger than the other
These signs can indicate bleeding or swelling in the brain, which requires immediate imaging and potentially surgical intervention. They can appear hours after the initial injury, which is why close monitoring during the first 24 to 48 hours matters so much. Loss of consciousness at the time of injury, while alarming, isn’t always present with concussion and isn’t required for diagnosis. Conversely, a brief loss of consciousness alone doesn’t automatically mean the injury is severe.
How All the Pieces Fit Together
No single test confirms a concussion. Diagnosis comes from layering multiple sources of information: what happened (the mechanism of injury), what you’re experiencing (symptoms), how your brain performs on structured tasks (cognitive testing), and how your body responds to physical challenges (balance and eye tracking). A clinician weighing all of this together, ideally comparing results against a pre-injury baseline when one exists, makes the call.
Having a baseline assessment on file, taken before any injury occurs, makes diagnosis significantly more accurate. Many sports programs now require preseason baseline testing for this reason. Without a baseline, clinicians rely on normative data for your age and compare your performance to population averages, which works but is less precise. If you participate in contact sports or activities with concussion risk, getting a baseline assessment done is one of the most practical steps you can take.