Leading experts propose a new framework for diagnosing traumatic brain injury
By Conor Gormally. This blog post is an expanded version of an article in the 5/29/25 Concussion Update Newsletter; please consider subscribing.
In a significant paradigm shift, 50 years in the making, 94 experts from 14 countries have proposed a new, multidimensional framework for classifying traumatic brain injury (TBI). The existing classification system utilizes the Glasgow Coma Scale (GCS), a 15-point scale that measures visual, verbal, and motor responsiveness, to classify TBIs as “mild, moderate, or severe.” The new framework proposed, CBI-M, consists of four pillars: Clinical assessment, Biomarker testing, Imaging, and Modifier, the latter capturing injury-, patient-, and social-environmental-related information. This new framework is an attempt to give providers (and patients) a more nuanced understanding of their injury, prognosis, and recovery needs. In this Policy View paper published in The Lancet Neurology, authors Geoffrey T. Manley et al. outline the structure and rationale for the CBI-M framework, including proposed diagnostic documentation for each pillar.
The terms “mild, moderate, and severe” further carry their own stigmas that can worsen patient outcomes. Patients with “mild” TBIs often report struggling to get providers to take their symptoms seriously and can spend months or years trying to get appropriate care. On the other end of the spectrum, some patients with severe TBI may be “given up on,” and taken off life support after only a few days; those who do go on to make full recoveries and their families still live with having faced a decision on removing life support.
While the CBI-M framework appears to constitute a significant improvement over solely using GCS to indicate “mild, moderate, or severe,” it is not finalized and will need to be validated through field testing in a wide variety of settings. There are also concerns about the global applicability of this framework, particularly in areas with limited resources and lower access to imaging tools and the necessary equipment for processing biomarker samples. Additionally, the authors acknowledge that this framework is also limited for patients outside of the acute window, a challenge magnified by findings that as many as 42% of patients with any severity of TBI don’t seek care immediately after injury.
The new proposed framework consists of four pillars: clinical, biomarker, imaging, and modifier (CBI-M). Assessing the clinical pillar is the highest priority. Next, if the clinical pillar indicates an obvious need for imaging, providers should prioritize imaging over biomarkers; biomarkers are more relevant when providers are uncertain about the need for imaging. The modifier pillar serves as a catch-all for relevant modifiers related to the injury, categorized into three classes of factors: injury-related, patient-related, and community and society-related. Some components of the modifier pillar (e.g., mechanism of injury, secondary injury, fall risk) should be assessed acutely, but others that are likely more relevant to the recovery process (e.g., mental health history or alcohol and substance misuse) may be assessed later.
Why a need for a new system?
The GCS is still an important and clinically relevant tool despite its age (it was introduced in 1974). However, as our understanding of concussions has evolved, the limitations of a solely GCS-based classification into three categories have become increasingly apparent.
Bucketing an injury that exists on a continuum into “mild, moderate, or severe” fails to capture important information about injury severity, and classification based on a single clinical measure (GCS) ignores other tools that can help create a more detailed injury profile. Additionally, the classification of “mild, moderate, or severe” is too simplistic for researchers to use meaningfully when selecting patients for treatment clinical trials.
The Pillars
The clinical assessment pillar still includes the GCS but also adds assessments of pupillary reactivity, post-traumatic amnesia (PTA), and signs & symptoms. The authors explain that PTA is a strong predictor of outcomes and that documenting signs and symptoms can aid in prognosis and recommendations for continued care.
The biomarker pillar suggests testing for at least one of three common biomarkers within 24 hours of injury: GFAP, UCH-L1, and S100B. GFAP and UCL-1 have been cleared for clinical use in the US and Europe, and low levels of any of these three can effectively indicate a sufficiently minimal risk of a brain bleed or other intracranial injury, ruling out the need for a CT scan and reducing costs and radiation exposure for many patients. The authors acknowledge that more research and standardization are needed to establish the clinical utility, cost-effectiveness, and accuracy of these biomarkers. While additional uses for these and other biomarkers are under research (including assessing microstructural damage that wouldn’t be visible on a CT scan), their effectiveness is not sufficiently established to be included in the guideline.
While the imaging pillar focuses on CT scans, the most commonly used imaging type in acute settings, it also includes MRIs, which are sometimes used acutely to limit radiation exposure to pediatric patients and are increasingly used for patients struggling with chronic symptoms. The imaging component of this framework evaluates various types of hemorrhages (active bleeds in the brain) and hematomas (areas where blood has pooled in the brain, commonly resulting from hemorrhages), as well as skull fractures. The imaging framework also evaluates for traumatic axonal or microvascular injury; this term encompasses two diagnoses: traumatic axonal injury and diffuse axonal injury.
The modifier pillar includes relevant injury modifiers such as a patient’s mechanism of injury, whether there was a secondary injury, medical history and medication, mental health status, substance misuse, employment status, language barriers, living situation, stressful circumstances, and social factors like health insurance, transportation issues, and food insecurity. The authors aim to better capture the biological, psychological, social, and environmental contexts in which patients exist, thereby enabling more accurate prognoses and more effective individualized care.