Background Cranial CT (CCT) is the gold standard to rule out traumatic brain injury. The serum level of the protein S-100B has recently been proposed as promising marker of traumatic brain injury. We prospectively investigated whether it might be a reliable tool for CCT triage in mild brain injury at a peripheral trauma centre with limited CT resources.

Methods Patients with mild head injury and a Glasgow Coma Score of 13–15 admitted to the emergency department of a peripheral trauma centre were enrolled. Blood samples for S-100B analysis were obtained after clinical evaluation. The cut-off level for positive S-100B was 0.105 μg/l. All patients underwent CCT. The relationship between clinical findings, CCT results and S-100B levels was evaluated.

Results 233 patients were enrolled. Median time between injury and sampling was 137 min. CCT was positive in 22 (9%) patients. Of these, 19 (8%) had positive serum S-100B levels. Overall, S-100B had a specificity of 12.2% and a sensitivity of 86.4%, with a positive predictive value of 12.8% and a negative predictive value of 85.7% as a selection tool for CCT triage in patients with mild head injury.

Conclusion The S-100B serum level showed a high sensitivity and negative predictive value in the screening of patients with mild head injury. The use of serum S-100B as a biomarker for CCT triage may improve patient screening and decrease the number of CCT scans performed. This would reduce unnecessary radiation exposure and free up capacity in the emergency rooms of peripheral hospitals to enable them to cope better with multiple admissions.