Three polyethylene glycol dependent methods for the detection of circulating immune complexes in pathological sera: Comparison with the Raji cell method

A composite method using polyethylene glycol (PEG) and different markers for detecting circulating immune complexes (CIC) is described. The markers used are bovine conglutinin (RK-BA), C1q (C1q-BA) and IgG, IgM quantitation of PEG precipitate (RID-Ig). A composite scoring system is used in interpreting results from individual assays. The sensitivity of multiple PEG methods (MPM) was determined in 418 serum samples and compared with Raji cell assay in 204. Correlations between individual assays, viz., RK-BA, C1q-BA, RID-Ig and Raji cell test in several disease conditions including rheumatoid arthritis, glomerulonephritis, post-renal transplantation, maintenance haemodialysis, multiple sclerosis and normal pregnancies were computed. The relative discriminatory ability of a single PEG technique to differentiate normal from pathological sera in these disease states was observed in comparison with the composite PEG index. This index gives an improved assessment of abnormal sera, is simple and sensitive and has some advantages over biological techniques such as the Raji cell assay.