Concussion Classification in a Multicenter Patient Cohort: The Updated ACRM Diagnostic Criteria and Concordance With Physician Impression of Injury

Objective : The American Congress of Rehabilitation Medicine (ACRM) substantially revised its diagnostic criteria for mild traumatic brain injury (mTBI) in 2023, encompassing acute symptoms and positive clinical and laboratory examinations, in addition to immediate signs of injury. This study aimed to apply these criteria to a large, diverse cohort and compare the diagnostic determination to physician impression of injury. Setting : A network of 3 concussion specialty clinics in Ontario, Canada. Participants : A total of 1447 patients (61.0% female; median age = 26 years [IQR: 15-42 years, range: 3-87 years]; days post-injury (median: 23 IQR: [13-47, 0-349]) completed initial evaluations between June 28, 2024 and June 18, 2025. Design : Prospective observational study. Main Measures : Occurrence rates were calculated, and binary/ordinal logistic regressions were applied to determine if individual criterion endorsement or diagnostic outcome (“Definite,” “Suspected,” and “No mTBI”) was associated with age, sex, symptoms at clinical presentation, or days post-injury. Additionally, concordance with physician impression was assessed similarly. Results : Criteria for signs, symptoms, and clinical examinations were all more likely to be endorsed with increasing symptom severity at presentation, as was an ACRM diagnostic outcome of definite mTBI. Shorter time post-injury was associated with positive clinical/laboratory examinations and the presence of confounding factors, in addition to a definite diagnostic outcome. A total of 18.4% of cases were classified less definitively as mTBI by physician impression than by the updated ACRM diagnosis, with physicians tending toward underdiagnosis, particularly in patients reporting lower current symptom severity. Conclusion : Use of the ACRM criteria clinically to determine if an injury qualifies as mTBI may be less susceptible to bias from ongoing symptom reporting than the physician impression of the injury.