Quick answer
Traumatic brain injuries are grouped as mild (also called concussion), moderate or severe.[1] Clinicians often use the Glasgow Coma Scale (GCS), which scores eye, verbal and motor responses from 3 to 15: 13 to 15 is mild, 9 to 12 is moderate and 3 to 8 is severe.[2] “Mild” describes how the injury looks at the time it happens. It does not guarantee a quick recovery.[3]
The three levels
MedlinePlus describes three levels of TBI: mild TBI (also called a concussion), moderate TBI and severe TBI.[1] It notes that how much brain function is affected, and for how long, depends on how severe the TBI is, and that moderate to severe TBIs can cause life-long health problems.[1]
The Glasgow Coma Scale
The GCS is one of the most widely used clinical scales in neuroscience.[2] It evaluates three aspects of responsiveness, each scored separately and then added together:[2]
Eye opening (1–4)
- 4: Opens spontaneously
- 3: Opens to command
- 2: Opens to pain
- 1: No eye opening
Verbal response (1–5)
- 5: Oriented
- 4: Confused
- 3: Inappropriate words
- 2: Incomprehensible sounds
- 1: No verbal response
Motor response (1–6)
- 6: Obeys commands
- 5: Localizes pain
- 4: Withdraws from pain
- 3: Abnormal flexion
- 2: Abnormal extension
- 1: No motor response
The total score ranges from 3 (the lowest) to 15 (the highest).[2]
Mild: 13–15
Moderate: 9–12
Severe: 3–8
Other factors clinicians consider
The GCS is only one measure. MedlinePlus notes that how long a person stays unconscious may be a sign of how serious a TBI is.[1] Imaging also matters: NINDS explains that CT can show a skull fracture and bruising, bleeding or swelling, while MRI can pick up subtler changes a CT scan may miss.[4] A clinical review on post-concussive syndrome describes a “complicated” mild TBI as one with concussion symptoms plus CT findings such as bleeding or a fracture.[3]
What “mild” does and doesn’t mean
A mild TBI is classified as mild because of how the person responds at the time of injury. NINDS describes a concussion as a mild TBI that may be considered a temporary injury but could take minutes to several months to heal.[4] The StatPearls review estimates that about 15% of people with a mild TBI develop post-concussion syndrome.[3] NINDS also notes that standard tests can’t always detect damage from mild, concussive injuries.[4]
How common each level is
The CDC states that most TBIs that occur each year are mild TBIs or concussions.[5] A 2020 study in the Journal of Neurotrauma reports that 80% to 90% of patients who come to the emergency department with a TBI have a mild TBI (GCS 13 to 15), that fewer than 10% of that group have abnormalities on head CT, and that fewer than 1% of those need neurosurgery.[6]
This page provides general information from the sources listed below. It is not medical advice and is not a substitute for evaluation by a qualified healthcare provider. In an emergency, call 911.
Sources
- MedlinePlus Medical Encyclopedia. “Traumatic brain injury.” https://medlineplus.gov/ency/article/000799.htm
- Munakomi S, Margetis K, Iverson LM. “Glasgow Coma Scale.” StatPearls, NCBI Bookshelf. https://www.ncbi.nlm.nih.gov/books/NBK513298/
- Permenter CM, Fernández-de Thomas RJ, Sherman AL. “Postconcussive Syndrome.” StatPearls, NCBI Bookshelf. https://www.ncbi.nlm.nih.gov/books/NBK534786/
- National Institute of Neurological Disorders and Stroke. “Traumatic Brain Injury (TBI).” https://www.ninds.nih.gov/health-information/disorders/traumatic-brain-injury-tbi
- Centers for Disease Control and Prevention. “About Mild TBI and Concussion.” https://www.cdc.gov/traumatic-brain-injury/about/index.html
- Okonkwo DO, et al. “Point-of-Care Platform Blood Biomarker Testing of Glial Fibrillary Acidic Protein versus S100 Calcium-Binding Protein B for Prediction of Traumatic Brain Injuries: A TRACK-TBI Study.” Journal of Neurotrauma, 2020. https://pmc.ncbi.nlm.nih.gov/articles/PMC7698990/
Sources last checked: October 11, 2026
