Usefulness and analytical performances of complement multiplex assay for measuring complement biomarkers in plasma

•The complement system is implicated in 50+ diseases with various mechanisms of activation or deficiencies.•Accurately assessing the level of complement activation remains a challenge.•Quantifying complement activation fragments and proteins could provide an instantaneous snapshot of the cascade's activation state.•We presented the use of complement multiplex ELISA for simultaneously measuring 14 complement proteins.•The data presented here pave the way for the utilization of the multiplex ELISA technique for quantifying complement proteins and fragments. The complement system is involved in numerous diseases, through diverse mechanisms and degree of activation. With the emergence of complement targeting therapeutic, simple and accessible tools to evaluate the extent of complement activation are strongly needed. We evaluated two multiplex panels, measuring complement activation fragments (C4a, C3a, C5a, Bb, Ba, sC5b9) and intact components or regulators (C1q, C2, C3, C4, C5, FD, FP, FH, FI). The specificity of each measurement was assessed by using complement proteins depleted sera and plasma collected from patients with complement deficiencies. Normal values distribution was estimated using 124 plasma samples from healthy donors and complement activation profile was assessed in plasma collected from 31 patients with various complement-mediated disorders. We observed good inter-assay variation. All tested protein deficiencies were accurately detected. We established assay-specific reference values for each analyte. Except for C3, C4 and C4a, the majority of the measurements were in good agreement with references methods or published data. Our study substantiates the utility of the Complement Multiplex assay as a tool for measuring complement activation and deficiencies. Quantifying complement cleavage fragments in patients exhibiting classical or alternative pathway activation allowed evaluating the activation state of the whole cascade.