The ideal marker of organ damage or dysfunction must be specific and sensitive. Of paramount importance is also that it should be easily and reliably measured with clearly defined thresholds, and preferably independent of age, sex and other concurrent systemic disorders. In addition, the serum levels of the marker should correlate with the severity of disease so that it is possible to predict accurately recovery, further damage and the likelihood of permanent injury. The diagnosis, prognosis and natural history of central nervous system (CNS) injury relies on repeated clinical neurological examination and radiological techniques such as computed tomography (CT) and/or magnetic resonance imaging (MRI). A number of clinical scenarios exist in which the application of such assessments is not practical or feasible. Therefore, the benefits of having a reliable, sensitive and specific serum biomarker for diagnosing and predicting prognosis after CNS injury are self-evident [1]. This chapter will discuss the merits and the potential pitfalls of protein S-100β as a useful marker of CNS damage and dysfunction.

S-100 proteins

The S-100 protein family consists of 17 members [2]. These proteins are made of two subunit amino acid chains, α and β. S-100 ββ is found in high concentrations in glial and Schwann cells, S-100 α1β in glial cells and S-100 α1α1 in kidney, and striated and cardiac muscles. The isoform of main interest in brain damage is the homodimer which consists of two monomers (S-100 ββ) and which is usually abbreviated to S-100β.