3. In patients with mild TBI, are brain-specific serum biomarkers predictive of an acute traumatic intracranial injury?

• Level A recommendation. None specified.
• Level B recommendation. None specified.
• Level C recommendation. In mild TBI patients without significant extracranial injuries and a serum S-100B level less than 0.1 mcg/L measured within 4 hours of injury, consideration can be given to not performing a CT. (Of note: This test, however, has not yet received FDA approval for clinical use in the United States).

There are a number of brain-specific proteins that are released from neurons and from supporting cells as a result of traumatic brain injury. Enolase and tau are two examples of neuronal proteins, while S-100B, creatine kinase BB isoenzyme, and glial fibrillary acidic protein are released from astrocytes. From the above list, S-100B has been the most studied in TBI and seems to show the most promise as a biomarker for injury.

Several Class II studies have compared S-100B with head CT finding in an attempt to gauge sensitivity and specificity in conjunction with finding the proper cutoff level for the assay. Biberthaler et al. measured serum S100-B levels within 3 hours of injury in 1,309 patients with isolated mild TBI and correlated these to CT scan.¹⁸ The sensitivity of S-100B was found to be 0.99 (95% CI, 0.96 to 1.0) and the specificity 0.30 (95% CI, 0.29 to 0.31).

In a Class II study, Poli-de-Figueiredo et al. studied S-100B in 50 consecutive patients with mild TBI (2 had a GCS of 13).¹⁹ They reported a sensitivity of serum S-100B measured within 3 hours of injury to be 1.0 (95% CI, 0.8 to 1.0) and the specificity 0.²⁰ (95% CI, 0.11 to 0.35). With a higher cut-off of 0.2 mcg/L, S100-B performed similarly well.20

The studies reviewed suggest that brain specific biomarkers may have a role in determining which patients with head injury need neuroimaging. This might be of great value in resource utilization, especially in small facilities where CT is not readily available.

4. Can a patient with an isolated mild TBI and a normal neurologic evaluation result be safely discharged from the ED if a noncontrast head CT scan shows no evidence of intracranial injury?

• Level A recommendation. None specified.
• Level B recommendation. Patients with an isolated mild TBI who have a negative head CT result are at minimal risk for developing an intracranial lesion and therefore may be safely discharged from the ED. (There are inadequate data to include patients with a bleeding disorder, who are receiving anticoagulation therapy or antiplatelet therapy, or who have had a previous neurosurgical procedure in this population.)
• Level C recommendation. Mild TBI patients discharged from the ED should be informed about postconcussive symptoms.

Risk of neurologic deterioration after discharge remains of prime clinical importance. A well-designed prospective, multicenter study involving 39 hospitals and 1,292 mild TBI patients reported that, at 3-month follow-up, no patient with a negative CT developed a complication requiring hospitalization.²¹ A comprehensive literature review by af Geijerstam and Britton included more than 62,000 cases of mild TBI with a GCS of 15; only 3 patients who had a normal CT deteriorated after discharge thus supporting the safety of home discharge after normal head CT scan results.²²