Background: The Glasgow Coma Scale (GCS) classifies traumatic brain injuries (TBIs) as mild (14-15), moderate (9-13), or severe (3-8). The Advanced Trauma Life Support modified this classification so that a GCS score of 13 is categorized as mild TBI. We investigated the effect of this modification on mortality prediction, comparing patients with a GCS score of 13 classified as moderate TBI (classic model) to patients with GCS score of 13 classified as mild TBI (modified model).
Methods: We selected adult TBI patients from the Pennsylvania Outcome Study database. Logistic regressions adjusting for age, sex, cause, severity, trauma center level, comorbidities, and isolated TBI were performed. A second evaluation included the time trend of mortality. A third evaluation also included hypothermia, hypotension, mechanical ventilation, screening for drugs, and severity of TBI. Discrimination of the models was evaluated using the area under receiver operating characteristic curve (AUC). Calibration was evaluated using the Hosmer-Lemershow goodness of fit test.
Results: In the first evaluation, the AUCs were 0.922 (95% CI, 0.917-0.926) and 0.908 (95% CI, 0.903-0.912) for classic and modified models, respectively. Both models showed poor calibration (p < 0.001). In the third evaluation, the AUCs were 0.946 (95% CI, 0.943-0.949) and 0.938 (95% CI, 0.934-0.940) for the classic and modified models, respectively, with improvements in calibration (p = 0.30 and p = 0.02 for the classic and modified models, respectively).
Conclusion: The lack of overlap between receiver operating characteristic curves of both models reveals a statistically significant difference in their ability to predict mortality. The classic model demonstrated better goodness of fit than the modified model. A GCS score of 13 classified as moderate TBI in a multivariate logistic regression model performed better than a GCS score of 13 classified as mild.