DEVELOPMENT AND VALIDATION OF AN AUTOMATED PARTICLE-ENHANCED NEPHELOMETRIC IMMUNOASSAY METHOD FOR THE MEASUREMENT OF HUMAN PLASMA C1Q

We have developed a sensitive immunoassay based on latex particle aggl utination for measuring C1q concentrations in human plasma. In this si mple and fast particle-enhanced immunoassay, we used carboxylated late x particles (diameter 210 nm) covalently coated with F(ab')(2) fragmen ts of anti-C1q antibodies. These particles are incubated with diluted sample (400-fold) for 6 min at room temperature, with the resulting ag glutination quantified by measuring the change of light-scatter produc ed. The assay has been automated on the Behring nephelometer analyzer with a sampling rate of 150 samples/hr. This assay generates a standar d curve in the range of 24-775 mg/L, showing intraassay and interassay precision of <8% and <10%, respectively. Dilution linearity was valid ated throughout the dynamic range of the assay. There were no interfer ences from bilirubin, Intralipid, haemoglobin, and rheumatoid factor. Results obtained in 45 clinical samples correlated well with those obt ained by a commercial radial immunodiffusion method (r = 0.936), and w ith those obtained by the Behring immunoprecipitation nephelometric te st (r = 0.950). The mean concentration in plasma from healthy subjects was 180 mg/L and the reference interval was from 128 to 237 mg/L. Thi s latex nephelometric procedure is a convenient method and an interest ing alternative to other immunoassays for routine measurement of human C1q. (C) 1995 Wiley-Liss, Inc.