Neuro biomarker levels measured with high-sensitivity digital ELISA differ between serum and plasma.

Aim: Digital ELISA-based assays for blood biomarkers of neurological disease are on the verge of clinical use. Here, we aimed to determine whether different preanalytical blood processing techniques influence results. Materials & methods: Concentrations of neurofilament light chain (NfL), Tau and amyloid beta (A beta) were measured in human plasma and serum specimens using digital ELISA and compared between blood products. Measured levels of NfL were highly equivalant between serum and plasma in all analyses, however, measured levels of Tau and A beta were consistently lower in serum relative to plasma. Conclusion: Tau and A beta are likely lost during clotting in serum preparations, and should be assayed in plasma to get an accurate measure of circulating levels.