Novel nephelometric assay for measurement of complement 3d.

Background This report describes a nephelometric assay for measuring complement 3d (C3d). Methods C3d was separated from C3 and the other C3 split products by polyethylene glycol precipitation. The supernatant containing C3d was then measured by rate nephelometry in a Beckman Immage rate nephelometer using a specific antibody. Calibration was performed with dilutions of a standard, which was obtained by incubating a serum pool at 37degreesC for 7 days. This incubation step allowed the activation and breakdown of C3 into C3d. Results The assay was linear across the normal and pathological range. Precision studies showed within-run and between-run coefficients of variation of <5% and <6%, respectively. The nephelometric results are comparable with those obtained by radial immunodiffusion. Neither haemoglobin nor lipids interfere with the assay.