Discrepancies in plasma levels of complement components measured by a newly introduced commercially available magnetic bead technique compared to presently available clinical reference intervals

BACKGROUND: Complement system aberrations are implicated in numerous pathological conditions. Techniques used in complement diagnostic include monitoring of individual proteins, activation products or function using different types of immunoassays. Most recent techniques include multiplex assays which enable simultaneous detection of multiple complement components or activation products in the same sample thereby saving both sample volume and time. MATERIALS AND METHODS: We have tested the performance of the commercially available Human Complement Magnetic Bead multiplex assay MILLIPLEX MAP H (EMD Millipore Corporation, Billerica, MA, USA) for simultaneous determination of C1q, C4, C3, factor B, properdin and factor H as well as MBL, C2, factor D, factor I, C5 and C9 using plasma from 68 healthy blood donors. RESULTS: The main observation was very low levels of C3 determined by the MILLIPLEX assay: median value 16.4 mg/L (range 7.7-57.4) compared to the present reference value of 670-1290 mg/L used in the clinic (i.e., 60-fold lower). Discrepancies (although not as pronounced as for C3) were also found for C1q, factor B, factor H, C2 and C9. CONCLUSION: The MILLIPEX assay is highly inaccurate regarding C3 and less reliable for several other analytes, and implies that the company should reconstruct their assay for C3 since the results are not on par with the standard of other techniques used today.