[Determination of circulating immune complexes: comparison between agglutination inhibition and C1Q precipitation in polyethylene-glycol-EDTA (author's transl)].

Three different methods for the determination of circulating immune complexes were compared : precipitation of radioiodinated C1q in polyethyleneglycol-EDTA, inhibition of IgG-coated latex particles agglutination by C1q or polyclonal rheumatoid factor. Normal values and their upper limits as well as the reproducibility of each technique are presented. The possible effect of several factors was investigated : age, sex, anticoagulants, freezing and thawing, contamination by DNA or endotoxin. Comparison of the results obtained with normal or pathological sera revealed a positive correlation between the three techniques. However, the discrepancies noted with some sera make the use of at least two different methods highly recommendable for the study of circulating immune complexes in disease.