Differential effects of the Glasgow Coma Scale Score and its Components: An analysis of 54,069 patients with traumatic brain injury

Introduction: The Glasgow Coma Scale (GCS) is widely used in the assessment of clinical severity and prediction of outcome after traumatic brain injury (TBI). The sum score is frequently applied, but the differential influence of the components infrequently addressed. We aimed to investigate the contribution of the GCS components to the sum score, floor and ceiling effects of the components, and their prognostic effects.

Methods: Data on adult TBI patients were gathered from three data repositories: TARN (n=50,064), VSTR (n=14,062), and CRASH (n=9,941). Data on initial hospital GCS-assessment and discharge mortality were extracted. A descriptive analysis was performed to identify floor and ceiling effects. The relation between GCS and outcome was studied by comparing case fatality rates (CFR) between different component-profiles adding up to identical sum scores using Chi²-tests, and by quantifying the prognostic value of each component and sum score with Nagelkerke's R² derived from logistic regression analyses across TBI severities.

Results: In the range 3-7, the sum score is primarily determined by the motor component, as the verbal and eye components show floor-effects at sum scores 7 and 8, respectively. In the range 8-12, the effect of the motor component attenuates and the verbal and eye components become more relevant. The motor, eye and verbal scores reach their ceiling-effects at sum 13, 14 and 15, respectively. Significant variations were exposed in CFR between different component-profiles despite identical sum scores, except in sum scores 6 and 7. Regression analysis showed that the motor score had highest R² values in severe TBI patients, whereas the other components were more relevant at higher sum scores. The prognostic value of the three components combined was consistently higher than that of the sum score alone.

Conclusion: The GCS-components contribute differentially across the spectrum of consciousness to the sum score, each having floor and ceiling effects. The specific component-profile is related to outcome and the three components combined contain higher prognostic value than the sum score across different TBI severities. We, therefore, recommend a multidimensional use of the three-component GCS both in clinical practice, and in prognostic studies.