Mild traumatic brain injury (mTBI) is a very common reason for presentation to pediatric emergency departments. So as not to overlook the risk of complications, which occur at a rate of 0-7%, measures such as cranial computed tomography (CCT-scan) and/or short inpatient observation are prescribed. Ultimately, the majority of these measures could be avoided and a large Australian cohort shows that the risk of brain tumors is 2.44 times higher for children who had a CCT-scan (3.24 for age 1-4 years). Assay of a sensitive biomarker in blood, such as the S100B protein, has the potential to reduce the number of these unnecessary measures.

Based on initial results from a previous prospective study, a multicenter interventional study will be necessary to validate the routine use of this biomarker .The ultimate goal is to include serum S100B assay in the current recommendations for m traumatic brain injury (mTBI) management based on the study of Kupperman et al. (2009), as mTBI accounts for 5-8% of pediatric emergency admissions in France (60-100 per 100,000 children). The study of Kuppermann et al. strongly dictated the recommendations for mTBI management by the French Society of Emergency Medicine (SFMU) . Then, from these 2 publications, the French Society of Pediatrics (SFP) redacted their recommendations after adjustment method recommendations for clinical practice, used by the French High Authority of Health (HAS) .

The use of serum S100B assay as part of the management of pediatric mTBI should make it possible to reduce the number of additional examinations, in particular a 30% reduction in the number of CCT-scans, with a resultant reduction in radiation exposure, known to be a risk factor for cancer. The study protocol corresponds to a diagnostic prospective, controlled, multicenter study using a randomized stepped wedge cluster design, in which pediatric patients (aged ≤ 16 years) presenting to the pediatric emergency room for mTBI with a GCS score of 15 will benefit from usual care ("conventional management" arm) in the control group, and from S100B management in the interventional group.

Inclusion Criteria:

• Age ≤ 16 years Therapeutic management within 3 hours after TBI

GCS score of 15 classically requiring hospitalization and/or CCT-scan as per SFP recommendations (Lorton et al., 2014). These criteria are:

• For children aged under 2 years (CCT-scan or hospitalization recommended according to physician's evaluation):
• Parietal or occipital scalp hematoma,
• Loss of consciousness for more than 5 seconds,
• Trauma due to serious accident (road accident with passenger ejected from vehicle or death of another person or rollover; pedestrian hit by a moving vehicle; cyclist not wearing a helmet; fall from a height greater than 0.9 meter),
• Abnormal behavior in the opinion of parents.
• For children 2 years and older (CCT-scan or hospitalization recommended according to physician's evaluation):
• Loss of consciousness at time of accident,
• Vomiting,
• Trauma due to serious accident (road accident with passenger ejected from vehicle or death of another person or rollover; pedestrian hit by a moving vehicle; cyclist not wearing a helmet; fall from a height greater than 1.5 meter),
• Severe headache.

Exclusion Criteria:

• Patient already enrolled in another therapeutic trial with drug administration Down syndrome Melanoma Refusal of child Refusal of parents or legal guardian Trauma more than 3 hours earlier GCS score of 13 or 14, or signs of skull fracture or lesions of the skull base (CCT-scan recommended)

Children with TBI not requiring hospitalization and/or CCT-scan as per SFP recommendations (Lorton et al., 2014). This group is defined by the absence of the following criteria:

• GCS score different from 15,
• Age < 3 months,
• Seriousness of accident:
• road accident with passenger ejected from vehicle or death of another person or rollover,
• pedestrian hit by a moving vehicle,
• cyclist not wearing a helmet.
• Fall:
• of more than 0.9 m before age 2 years,
• of more than 1.5 m after age 2 years.
• Loss of consciousness for 5 seconds or more,
• Inconsolable crying,
• Agitation, drowsiness, feeling "slowed down", obnubilation,
• Vomiting or headache,
• Facial or cranial hematoma,
• Otorrhea, rhinorrhea,
• Child under 2 years old,
• Loss of consciousness for less than 5 seconds,
• Unusual behaviour,
• Concern of family members