Objectives: S100B is an established marker of brain damage. Used in the context as a biochemical marker, S100B denotes a measurement of all S100 proteins, including at least one S100B monomer, i.e. the sum of the two dimers S100A1B and S100BB. Almost all published studies are based on this "sum concentration". However, the brain specificity of S100B has been questioned and increased serum levels have also been reported after trauma without head injury. Since the S100B monomer dominates in the brain, we hypothesised that the S100BB dimer should be better related to outcome after severe traumatic brain injury than S100A1B or the "sum concentration".
Methods: Daily serum samples were collected from 59 patients with severe traumatic brain injury. Three different ELISA methods were used for measurements of S100B, S100A1B and S100BB respectively. Outcome was assessed after one year and categorised according to the Glasgow Outcome Scale.
Results: Serum levels of S100B, S100A1B and S100BB followed the same temporal course, with early maximum and rapidly decreasing values over the first days after the trauma. Maximum serum concentrations of each of the parameters were increased in the patient group with an unfavourable outcome compared with those with a favourable outcome (p = 0.01, 0.006 and 0.004, respectively).
Conclusion: Both S100A1B and S100BB were related to outcome after severe traumatic brain injury. Even though this study is small, it seems unlikely that separate analyses of the dimers are of any advantage compared with measuring S100B alone.