Introduction: Cytokines are humoral regulatory molecules that act together in immunologic pathways. Monitoring cytokines and their variations within physiologic ranges is critical for biomarker discovery. Therefore, we evaluated the performance characteristics of 72 analytes measured by multiplex cytokine immunoassay, with an emphasis on the differences of analytes measured in serum compared to plasma, and, in plasma, on the impact of anticoagulants on the cytokine measurement.
Methods: We used fluorescent bead-based (Luminex) immunoassay kits to simultaneously measure 72 analytes. We tested serum and plasma samples from 11 matched donors. Plasma samples were anti-coagulated with sodium heparin, sodium citrate dextrose and ethylene diamine tetra-acetic acid (EDTA), respectively.
Results: Of the 72 cytokines, 12 were undetectable in all types of specimen samples. Nineteen analytes, including PDGF-bb, IL-4, IL-8, IL-9, FGF-b, PAI-1, CXCL-5, CCL-5, CD40L, EGF, VEGF, IL-2ra, IL-3, SDF-1a, PCT, MCP-3, GIP, IL-16 and fibrinogen, showed significant differences between measurements in serum and all types of plasma, regardless of anticoagulant. Among plasma samples, 10 analytes (eotaxin, SCGF-b, MCP-1, SCF, MIP-1b, VEGF, RANTES, PDGF-b, PAI-1 and ITAC) showed significantly higher concentrations in heparinized plasma compared to citrated and EDTA plasma. IP-10, and CTAK were the only 2 cytokines that presented different concentrations in citrate and EDTA plasma.
Conclusions: With their small volume, low cost per test, and multiplex capacity, Luminex-based cytokine assays have enormous potential utility for screening in epidemiologic studies. In our study, we showed that many cytokines' concentrations differed between serum and plasma samples, and that different anticoagulants used in preparation of plasma samples also affected the measurement of some cytokines. There was no optimal sample preparation that was clearly superior for the measurement of all analytes measured. Ultimately, the utility of cytokine measurement, as biomarker or to monitor the immune system, will depend on attention to detail in the collection and processing of samples in addition to assay precision.
Published by Elsevier Ltd.