Traumatic brain injury: It is all about definition

Background: TBI may be defined by different methods. Some may be most useful for immediate clinical purposes, however less optimal for epidemiologic research. Other methods, such as the Abbreviated Injury Score (AIS), may prove more beneficial for this task, if the cut-off-points for their categories are defined correctly. Objective: To reveal the optimal cut-off-points for AIS in definition of severity of TBI in order to ensure uniformity between future studies of TBI. Results: Mortality of patients with TBI AIS 3, 4 was 1.9% and 2.9% respectively, comparing with 31.1% among TBI AIS 5+. Predictive discrimination ability of the model with cut-off-points of 5+ for TBI AIS (in comparison with other cut-off-points) was better. Patients with missing Glasgow Coma Scale (GCS) in the ED had an in-hospital mortality rate of 11.5%. In this group, 25% had critical TBI according to AIS. Normal GCS didn’t indicate an absence of head injury, as, among patients with GCS 15 in the ED, 26% had serious/critical TBI injury. Moreover, 7% of patients with multiple injury and GCS 3–8 had another reason than head injury for unconsciousness. Conclusions: This study recommends the adoption of an AIS cut-off ≥ 5 as a valid definition of severe TBI in epidemiological studies, while AIS 3–4 may be defined as ‘moderate’ TBI and AIS 1–2 as ‘mild’.