In other words, day-of-injury GFAP may have strong utility as a diagnostic biomarker of TBI but studies to date have shown limited utility of day-of-injury GFAP as a prognostic biomarker.8 Regardless, the present analysis suggests that, even in patients evaluated for TBI in the emergency department with negative head CT scans and lower GFAP, depressive disorder onset (or worsening) can occur and all patients should be monitored for these sequelae. Here, GFAP is linked to depressive disorder.