Analysis of protein S-100B in serum: a methodological study

Background: Dysfunction and damage of the human central nervous system can be detected with biochemical markers, and protein S-100B is the best-established such marker. The aim of this study was to evaluate whether the protein is stable during longterm storage, to establish reference values for the new Elecsys((R)) S100 test and to compare this new method with the Liaison((R)) Sangtec((R)) 100 test. Methods: We analysed blood samples from 118 blood donors and 196 patients with subarachnoid haemorrhage or head injury. The long-term stability of S-100B in frozen serum samples was evaluated with repeated analysis in 1997 and 2003 using an immunoradiometric assay. Method comparison between the Liaison((R)) Sangtec((R)) 100 and Elecsys((R)) S100 tests was performed using Bland-Altman difference plots. Results: Serum concentrations increased significantly during long-term storage (mean difference 0.15 mu g/L; +/- 2 SD, 0.55 mu g/L). Serum measurements using the Elecsys ((R)) S100 method in 118 healthy blood donors showed S-100B levels between 0.02 and 0.08 mu g/L (mean 0.05). The 95th percentile was 0.07 mu g/L. The Liaison ((R)) Sangtec((R)) 100 test usually measured higher concentrations than the Elecsys((R)) S100 method, and the difference between the two methods increased with increasing concentrations. The mean difference between the methods was 0.14 mu g/L (+/- 2 SD, 0.39 mu g/L). Conclusions: Protein S-100B is not stable during longterm storage and the two analytical methods are not interchangeable.