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One minute you’re skiing at Snoqualmie Pass, the next you’re in the ER with a concussion after a wipeout. Accidents can happen to anyone, even if you’re being careful — and anyone can get a traumatic brain injury like a concussion.
Your doctor says it’s mild, but injuring your brain doesn’t feel mild. Sure, doctors might see similar cases regularly, but this is significantly impacting your life. Your head hurts, you’re having trouble focusing and you’re not sleeping as well. After days of this, you’re starting to wonder just how mild your injury really is.
Unfortunately, there are many different clinical definitions of mild brain injury used by doctors, meaning that, depending on the definition followed, one doctor may diagnose you with mild brain injury while another doctor may diagnose you with moderate brain injury.
Why would your diagnosis differ if your problems and symptoms are the same?
According to Christine Mac Donald, PhD, professor and vice chair of neurological surgery at UW Medicine, the stumbling block is the many clinical definitions used to classify brain injuries.
“We use the terms mild, moderate and severe to describe traumatic brain injuries,” she says. “But these terms aren’t much help when we try to understand what a patient’s condition will look like in the future.”
Mac Donald leads a team, sponsored by the National Institutes of Neurological Disorders and Stroke, dedicated to improving the traumatic brain injury (TBI) classification system and patient care. The goal, she says, is to create clear, well-defined diagnostic criteria that will help doctors speak the same language when they diagnose TBIs, regardless of where you go for care.
Why does TBI classification matter for patients?
Like cancer, TBI is a blanket term. It can apply to any injury that involves damage to brain tissue and the surrounding blood vessels.
But, while doctors can tell you what type of cancer you have, what stage it is, and even which genes may be involved, that level of detail doesn’t consistently get communicated with TBI. There is no universally accepted diagnostic criterium that is used across medical specialties to diagnose and treat brain injuries.
That means hospitals and doctors use many different clinical definitions to diagnose TBI. The only consistent terms are mild, moderate and severe, which are vague and can negatively affect patients in several ways.
First, it can create confusion and misunderstanding for patients. If someone is told they ‘just’ have a concussion, a type of mild TBI, there is often an expectation that they should be fine — but many people still struggle, which leads to further challenges with recovery.
Second, if a patient is diagnosed with a mild TBI, they may struggle to get the rehabilitative care they need, purely because of how the TBI is referenced in their medical records.
“Insurance companies use the terms we have for TBI to justify how many days of rehab they’ll pay for,” Mac Donald says. “If a TBI isn’t classified correctly, patients may lose out on care that can improve their quality of life. These unclear definitions have a real-world impact.”
Lastly, large studies have found that the terms mild, moderate and severe don’t help inform long-term outcomes and recovery. Many patients with a ‘mild’ brain injury often have lasting symptoms, while an impressive number of patients with a ‘severe’ brain injury end up doing quite well.
Reimagining how TBIs are diagnosed
So, how do doctors currently diagnose TBIs? For roughly 50 years, doctors have primarily used the Glasgow Coma Scale (GCS) to evaluate how alert someone is after a head injury: A mild brain injury scores between 13 and 15, a moderate brain injury between 9 and 12, and a severe brain injury between 3 and 8.
This scale reviews eye movement, verbal answers to questions and physical movements — it’s helpful for knowing if someone needs emergency care, but it doesn’t tell you much about the brain injury beyond the patient’s level of consciousness, which can be influenced by other factors such as intoxication.
“Imaging is the ground truth for TBI diagnosis and can pick up nearly 30 types of brain lesions that a head injury can cause,” Mac Donald says. “But imaging has limitations; there’s no guarantee you’re seeing everything.”
That’s why Mac Donald and her colleagues designed a more comprehensive method to diagnose TBIs, which they published in the June 2025 issue of The Lancet.
This new framework includes using these things in combination:
- Clinical measurements (GCS results and details about how your pupils respond to light)
- Biomarkers (specific proteins that appear in the blood when you have a TBI)
- Imaging (measurements of brain damage seen on CT and MRI images)
- Modifiers (factors that can influence outcomes, such as psychological health history, neurodegenerative disease, obesity and other health conditions)
According to Mac Donald, this will give doctors the added information they need to classify brain injury more accurately and make sure you get the care you need.
Why traumatic brain injury research matters
A more detailed classification system — and more research on TBIs in general — will help doctors know which treatment options are best for an individual, plus help people with brain injuries better understand what their recovery might look like. It can also help people get better care in the interim.
“Traumatic brain injury is complex. It’s a condition that can happen to anyone. It can happen anywhere and everywhere in the brain. It doesn’t have a specific pattern like a neurodegenerative disease like Alzheimer’s,” Mac Donald says. “Our best chance at improving detection and treatment is to have a flexible model that provides more information to help us completely classify a patient’s head injury.”
The brain is still largely a mystery, despite all the scientific advances toward understanding it. Getting as specific as possible when diagnosing TBI and using a universal definition could help ensure that more people with a brain injury are given the most opportunities for recovery.
