Objectives : Blood biomarkers GFAP and UCH-L1 have recently been FDA approved as predictors of intracranial lesions on CT after mild traumatic brain injury (mTBI). However, the vast majority of mTBI cases are CT negative, and no biomarkers are approved to assist diagnosis in these individuals. Here we aimed to determine the optimal combination of blood biomarkers to assist mTBI diagnosis in otherwise healthy adults aged under 50 presenting to an ED within 6h of injury. To further understand the utility of biomarkers, we assessed how biological sex, presence or absence of loss of consciousness and/or post traumatic amnesia (LOC/PTA), and delayed presentation, affected classification performance. Methods : Blood samples, symptom questionnaires and cognitive tests were conducted prospectively for mTBI participants recruited from The Alfred Hospital Level 1 Emergency & Trauma Centre and uninjured controls. Follow-up testing was conducted at 7 days. Simoa® quantified plasma GFAP, UCH-L1, Ta