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 37°C 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.
