Glial Fibrillary Acidic Protein and its breakdown products (GFAP-BDP) are brain specific proteins released into serum as part of the pathophysiologic response following traumatic brain injury (TBI). We performed a multicenter trial to validate and characterize the use of GFAP-BDP levels in the diagnosis of intracranial injury in a broad population of patients with a positive clinical screen for head injury. This multicenter, prospective cohort study included patients 16 to 93 years old presenting to 3 Level I trauma centers with suspected TBI (loss of consciousness, post-trauma amnesia, etc.). Serum GFAP-BDP levels were drawn within 24 hours and analyzed, in a blinded fashion, using sandwich enzyme-linked immunosorbent assay. The ability of GFAP-BDP to predict intracranial injury on admission CT as well as delayed MRI was analyzed by multiple regression and assessed by the area under the receiver operating characteristic curve (AUC). Utility of GFAP-BDP to predict injury and reduce unnecessary CT scans was assessed utilizing decision curve analysis. 215 patients were included, of which 83% suffered mild TBI, 4% moderate, and 12% severe; the mean age was 42.1± 18 years. Evidence of intracranial injury was present in 51% of the sample (median Rotterdam Score 2 (IQR 2)). GFAP-BDP demonstrated very good predictive ability (AUC= 0.87), and demonstrated significant discrimination of injury severity (OR 1.45, 95% CI 1.29-1.64). Use of GFAP-BDP yielded a net benefit above clinical screening alone and a net reduction in unnecessary scans by 12 to 30%. Used in conjunction with other clinical information, rapid measurement of GFAP-BDP is useful in establishing or excluding the diagnosis of radiographically apparent intracranial injury throughout the spectrum of TBI. As an adjunct to current screening practices, GFAP-BDP may help avoid unnecessary CT scans without sacrificing sensitivity.