A modified C1q deviation radioimmunoassay for use in a routine clinical laboratory.

Current clinical interest in circulating immune complexes defines a need to develop immune complex assays suitable for use in routine clinical immunology laboratories. We describe one such assay based on the principle of immune complexes binding to radiolabelled C1q, using commercially available IgG-coated latex particles for competitive binding. The assay is simple, rapid, cheap, reproducible and sensitive (5 micrograms/ml). Specificity for both antibody and antigen was demonstrated and clinical value was proven with defined clinical groups.