Analysis of serum and plasma identifies differences in molecular coverage, measurement variability, and candidate biomarker selection

Purpose To compare the use of serum and plasma in multiplex immunoassay analyses of 190 proteins and small molecules, and associated molecular pathways. We also tested whether differences between these biofluids can influence the identification of potential biomarkers in a preliminary study comparing bipolar disorder patients with controls. Experimental design Using multiplexed immunoassay analyses, we compared the measurement levels and interindividual variation of 190 proteins and small molecules between serum and plasma collected from 21 healthy individuals. We exemplify how this can impact on the outcome of biomarker discovery studies using a case study of 24 patients with bipolar disorder. Results Detection of analytes was similar for serum and plasma, although there were marked differences in measurement variability for 29 proteins and cortisol. When considering the disease cohort we identified six proteins that changed significantly in serum and ten in plasma with an overlap of two proteins. Conclusions and clinical relevance In spite of the similarities of coverage on a multiplexed platform for serum and plasma, there were important differences in interindividual variability, which can have significant impact on identifications made in biomarker studies.