Logistic regression analysis revealed that inclusion of GFAP was associated with greater classification of athletes with concussion from both contact sport controls (β = 12.298; 95% CI, 2.776-54.481; P = .001) and non–contact sport controls (β = 5.438; 95% CI, 1.676-17.645; P = .005) than SCAT-3 symptom severity score alone at the acute postinjury time point. Here, GFAP is linked to brain injury.