antibody biomarkers. It is critical to collect samples under well-defined protocols for both biomarker discovery and validation studies, especially because even within a panel of multiplexed biomarker assays, different biomarkers were affected very differently by these pre-analytical variables. Previous studies comparing plasma and serum have shown that the measurable levels of analytes may vary between the 2 sample

types (Miles et al., 2004). Quantifications with two common RA autoantibody assays, anti-cyclic citrullinated peptides (CCP) and rheumatoid factor (RF) have been demonstrated equivalent with either serum or plasma (Rantapaa-Dahlqvist et al., 2003). When sample handling variables, such as sample type (e.g., serum vs. plasma), room temperature storage, heat treatment, HSP tumor hemolysis, and repetitive freeze–thaw cycles, were evaluated on the performance of immunoassay detection of antibodies against Erysipelothrix rhusiopathiae ( Neumann and Bonistalli, 2009), no significant impact was found suggesting that immunoglobulin G antibody was stable in cases of common sample mishandling events. Autoantibodies are human immunoglobulins against an individual’s own proteins and should present similar characteristics to antibodies against bacteria. In fact, our results www.selleckchem.com/products/BIBF1120.html confirmed that antibodies appear to be stable biomarkers that were not largely affected by pre-analytical variables. The difference

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measurements in paired samples is largely within +/−15%. The impact of blood sampling (serum vs. plasma) was minimal for autoantibody quantification with correlation coefficients near 1.0. For the non-antibody protein biomarker assays, the difference between plasma and serum concentrations was dependent on individual biological characteristics of the proteins. Concentrations of some protein biomarkers were lower in plasma than in serum, e.g., VEGF-A, EGF, VCAM-1 and resistin, while other protein biomarkers exhibited no significant change. For CRP, we have observed a correlation of 1.00 between plasma and serum samples, with median difference of 12%. This result agreed with previous studies when CRP was measured in matched plasma and serum samples in protein biomarker measurements (Miles et al., 2004). For MMP-1, however, we observed a wide range of concentration changes between RA subjects, with 60% demonstrating increased concentrations in plasma and 40% of RA subjects showing decreased concentrations. The CVs of all duplicate measurements were less than 10% (data not shown), so that assay variability is not likely contributing to the diverse results. Protein biomarker concentrations are also greatly affected by post-collection sample handling methods. One can surmise that this is a result of blood cell lysis when samples had prolonged (> 12 h) contact with blood cells at room temperature (traditional conditions).