A concussion is identified primarily through observable symptoms and clinical evaluation, not brain scans. There is no single definitive test. Instead, identification relies on recognizing a combination of physical, cognitive, and emotional changes after a bump, blow, or jolt to the head or body. Symptoms can appear immediately or take hours to days to show up, which means monitoring after any head impact is just as important as the initial check.
Symptoms to Watch For
Most concussions announce themselves through a cluster of symptoms rather than one dramatic sign. Headache and dizziness are the most common, but the full picture spans physical, cognitive, and emotional changes. Physical symptoms include headache, nausea, blurry vision, sensitivity to light or noise, balance problems, and fatigue. Cognitive symptoms show up as difficulty concentrating, feeling mentally foggy, slowed thinking, and trouble remembering new information. Emotional changes can include irritability, sadness, nervousness, or feeling “off” in ways that are hard to pinpoint.
A person does not need to lose consciousness to have a concussion. In fact, most concussions happen without any loss of consciousness at all. What matters more is the overall pattern: if someone took a hit and now seems confused, sluggish, or just not themselves, that combination of changes is the clearest signal.
Some symptoms appear right away, while others may not surface for hours or even days after the injury. This delayed onset is why it’s important to keep watching someone after a head impact, even if they initially seem fine. New symptoms appearing the next morning, like trouble concentrating or a worsening headache, still point to a concussion.
How Professionals Evaluate a Concussion
Healthcare providers and athletic trainers use structured assessment tools to evaluate a suspected concussion. The most widely used in sports is the Sport Concussion Assessment Tool (currently in its sixth version, SCAT6), which tests several domains in sequence. It starts with observable signs and a check of basic neurological function, including eye movement and coordination. Then it moves to a symptom checklist, memory questions, concentration tasks like reciting digits backward or months in reverse order, and balance testing.
Balance assessment is a key piece. The modified Balance Error Scoring System has the person stand in specific stances with eyes closed while an evaluator counts errors. Timed tandem gait, which is walking heel-to-toe along a line, and dual-task gait, which is walking while performing a mental task simultaneously, round out the physical evaluation. A delayed memory recall test checks whether the person can remember a word list given earlier in the exam.
These tools work best when there’s a baseline for comparison. Many sports programs now test athletes before their season starts so that post-injury results can be measured against their normal performance. Without a baseline, clinicians compare results to population averages, which is less precise but still useful.
Why CT Scans and MRIs Often Look Normal
One of the most confusing aspects of concussions is that standard imaging usually shows nothing wrong. CT scans and MRIs are designed to detect structural damage like bleeding, skull fractures, or swelling. A concussion, however, is a functional injury. It disrupts how brain cells communicate and use energy without necessarily tearing or breaking anything visible on a scan.
What actually happens inside the brain is an energy crisis. The impact causes brain cells to release a flood of signaling chemicals, triggering a rush of charged particles across cell membranes. Restoring normal balance requires a surge of energy, but blood flow to the brain can drop significantly after a concussion, starving cells of the fuel they need. The brain burns through its glucose reserves quickly and then shifts into an energy deficit. This mismatch between energy demand and energy supply is what produces symptoms, and none of it shows up on a standard scan.
CT scans are still used after head injuries, but their purpose is to rule out something more dangerous, like a brain bleed, not to confirm a concussion. CT is fast, which makes it the go-to choice in emergency settings. If the CT is normal, that’s good news about bleeding and fractures, but it doesn’t mean there’s no concussion.
Blood Tests for Concussion
A relatively new option is a blood test that measures two proteins released by damaged brain cells. The FDA-cleared i-STAT TBI test detects levels of UCH-L1 and GFAP, proteins that leak into the bloodstream when brain tissue is injured. The test can be used within 24 hours of injury and helps clinicians decide whether a CT scan is needed. If protein levels are low, it’s less likely there’s structural bleeding that requires imaging. This doesn’t diagnose a concussion on its own, but it adds a useful data point, particularly in emergency departments trying to determine whether a scan is warranted.
Red Flags That Require Emergency Care
Most concussions resolve on their own, but certain symptoms after a head impact signal something more serious. These warrant an immediate trip to the emergency department:
- Seizures or convulsions
- Inability to recognize people or places
- Repeated vomiting
- Increasing confusion, restlessness, or agitation
- Loss of consciousness, excessive drowsiness, or inability to stay awake
- Slurred speech, weakness, numbness, or loss of coordination
- A headache that keeps getting worse and won’t go away
- One pupil noticeably larger than the other, or double vision
For infants and toddlers, the same red flags apply, plus inconsolable crying and refusal to eat or nurse. Young children can’t describe their symptoms, so behavioral changes carry more weight. A toddler who suddenly won’t eat, can’t be comforted, or seems unusually drowsy after a fall needs immediate evaluation.
Identifying a Concussion in Real Time
If you’re trying to assess someone on a field, at home, or at the scene of an accident, focus on a few practical checks. Ask them simple questions: what day is it, where are they, what happened just before the injury. Watch their eyes for unequal pupils or difficulty tracking a moving finger. Have them walk in a straight line and note any wobbling or unsteadiness. Ask if they have a headache, feel nauseous, or see spots.
Pay attention to how they behave over the next several hours. Someone who seemed fine at first but becomes increasingly foggy, irritable, or sleepy may be showing delayed concussion symptoms. Waking the person periodically during sleep in the first night after a significant head impact is a reasonable precaution, checking that they’re responsive and coherent.
What Happens After Identification
Once a concussion is identified, recovery follows a gradual, step-by-step process. For athletes, the standard return-to-play protocol involves six stages, each requiring a minimum of 24 hours before advancing to the next. It starts with a return to normal daily activities like school or work with no symptoms. Then comes light aerobic activity (five to ten minutes of walking or stationary cycling), followed by moderate activity with more head and body movement. Heavy non-contact exercise comes next, then full-contact practice, and finally competition.
If symptoms return at any stage, the person drops back to the previous step and waits before trying again. This graduated approach prevents reinjury during the vulnerable recovery window when the brain’s energy balance hasn’t fully restored. For non-athletes, the same principle applies in everyday life: a gradual return to mental and physical activity, guided by how you feel at each step.