Peripheral detection of S100β during cardiothoracic surgery: what are we really measuring?

Background S100β has been used in cardiac surgery to identify patients with postoperative neurologic complications. However, extracranial proteins may falsely elevate measurements of serum S100β;. Objectives of this study were (1) to quantify S100β levels in serum and pericardial cavity during coronary artery bypass grafting (CABG), and (2) to identify proteins recognized by standard immunodetection as S100β. Methods Systemic and pericardial cavity blood from 5 patients undergoing CABG were sampled before, during, and after cardiopulmonary bypass (CPB). A commercially available enzyme-linked immunosorbent assay (ELISA) kit was used to quantify S100β. Two-dimensional gel electrophoresis, Western blot, and mass spectroscopy were also performed to identify S100â and other proteins. Results Mean S100β levels measured by ELISA, systemic and pericardial cavity blood were (in ng • mL−1) 1.0 ± 0.46 and 111 ± 71 before CPB, 0.6 ± 0.11 and 113 ± 54 during CPB, and 1.7 ± 0.64 and 101 ± 42 after CPB, respectively. However, gel electrophoresis and Western blot analysis revealed proteins other than S100β to be present in the pericardial cavity giving a falsely elevated serum S100â levels measured by immunoassay. Mass spectroscopy of identified potential candidates revealed contaminants including haptoglobin I precursor, apolipoprotein A-1 precursor, complement factor B precursor, and complement C3 precursor. Conclusions S100β immunoassays are not specific for S100â and give a falsely elevated reading due to contaminants from the surgical field that cross react with the assayʹs antibody. This does not appear to be an issue in nonsurgical patients. Caution must be exerted when evaluating immunodetection results for low-abundance proteins under conditions where contamination of the sample is likely.