How Concussions Are Diagnosed

How many fingers am I holding up?
Steve Debenport / Getty Images

Diagnosing a concussion can be tricky. Although any degree of head trauma can cause one, the most common concussions—those that result from mild head injuries—do not involve identifiable bleeding or bruising in the brain.

This means that using a brain scan technique such as magnetic resonance imaging (MRI) or computed tomography (CT), which are done to diagnose a severe traumatic brain injury (TBI), isn't a viable way to diagnose a concussion.

Since brain scans can identify bruising or bleeding in the brain, but not the cellular damage thought to cause concussion symptoms, doctors must rely on a careful assessment of symptoms and neuropsychological function.

Sometimes this is done on-site, immediately after an injury, when an athlete experiences a blow or jolt to the head and a decision must be made quickly about whether he or she can safely get back into the game.

Concussion Testing

The symptoms of a concussion can vary greatly. Sometimes it's quite obvious that someone may have one. But just as often the symptoms are vague and subtle. A person may simply feel "off" or as if he's not "getting" things. In any case, getting a definitive diagnosis of a concussion typically requires looking at several factors.

Because there's no simple test for diagnosing a concussion, typically several steps are involved. The Weill Cornell Brain and Spine Center, for example, narrows it down to these: 

  • Testing for various types of amnesia. These include retrograde amnesia, which refers to a lack of memory about what happened just before a brain injury occurred, loss of consciousness, and post-traumatic amnesia. Post-traumatic amnesia is especially important because it will tell a doctor the most information about a patient's prognosis.
  • Determination of the severity of symptoms and how extensive they are. Often this is part of an on-site assessment of an athlete who's been injured on the field, using a standardized scale. The most common of these, the Sideline Concussion Assessment Tool, or SCAT-2, looks at symptoms, attention, memory; recent events in the game or event; and checks for problems with balance and coordination.
  • Examination for neurological symptoms. This may involve tests of strength, sensation, reflexes, coordination, and other neurological functions.

Pre-Concussion Testing

Besides diagnosing an initial concussion at the time of an injury, it's important for people who are going to participate in an activity—especially student-athletes who want to participate in a high-impact team sport such as football—to undergo pre-concussion testing. In fact, this usually is a requirement of high schools, colleges, and highly competitive travel teams. 

The main reason an athlete needs pre-concussion testing is that healthy individuals do not perform exactly the same on tests that measure skills such as speed, accuracy, and eye movements. This means that performance on a post-concussion test is not necessarily "good" or "bad" on its own, but must be based on whether or not there is a significant decline in comparison to the baseline that was set prior to the head injury.

If a student-athlete has a slower response or lower accuracy on a post-concussion test after a head injury, then the lower score could be a sign of a concussion. Along with a neurological examination and overall symptoms such as sleepiness, pain, or trouble concentrating, the results of a post-concussion test can be used to help determine whether the athlete has suffered from a concussion.

Pre-concussion testing generally includes a set of neuropsychological exams developed to assess and score a young athlete on skills that involve several aspects of his or her brain function. Pre-concussion tests include tasks that evaluate problem-solving, response time, speed, vision, and coordination.

There's no gold standard pre-concussion screening tool required by an authoritative medical or sports association. There are a variety of ways to establish a pre-concussion score, including an in-person clinical evaluation or a pre-set questionnaire. There also are a number of available skills tests on the market that can be used to establish a baseline score for a player before the season begins.

Pre-concussion tests may be scored by a computer or by a medical professional, depending on the type of examination and on the rules of the league or the school. The baseline results are recorded and saved so that if an athlete suffers from a suspected concussion, he or she can take a repeat test for comparison.

An example of computer-scored test was developed by researchers at the University of Pittsburgh's Sports Medicine Center and is called Immediate Post-Concussion Assessment and Cognitive Testing system, or ImPACT. This test measures an athlete's memory, reaction time, and processing speed in order to help determine when an athlete can safely return to sports after a head injury. The ImPACT program is currently used at many high schools and colleges, as well as by the National Football League and National Hockey League.


Hall E, Cottle J, Ketcham C, Patel K, and Barnes KP . "Concussion Baseline Testing: Preexisting Factors, Symptoms, and Neurocognitive Performance, J Athl Train. Jan 10, 2017. DOI: 10.4085/1062-6050-51.12.21

Thomas, RE, Alves, J, Vaska, MM, and Magalhaes, R. "SCAT2 and SCAT3 Scores at Baseline and After Sports-related Mild Brain Injury/Concussion: Qualitative Synthesis With Weighted Means.BMJ Open Sport & Exer Med. 2016;2:e000095. DOI: 10.1136/bmjsem-2015-000095

Weill Cornell Brain and Spine Center. "Diagnosing and Treating Concussion." Nov 2014.