[Detection of circulating immune complexes with the polyethylene glycol precipitation test: advantages and limitations of the method].

The precipitation test with 3.5% PEG has been used to reveal the presence of circulating immuno complexes (IC) in a sample of 130 blood donors. The asymmetry in the O.D. distribution has been corrected by the square root transformation. The positivity threshold has been fixed at the superior extreme of the 95% fiducial interval relative to the transformed data of the control sample, namely at 0.125 O.D.280nm. The correlation between O.D. values obtained with PEG-test and serum concentration of IgG, IgA, IgM, C3 has been studied in 50 of 130 blood donors, 53 patients with gastro-intestinal neoplasm, 73 patients with different forms of the rheumatic disease and 17 patients with cryoglobulinaemia. No significant correlation has been found in normal subjects. Instead, a positive correlation could be demonstrated between O.D. values and IgG concentration both in neoplastic, rheumatic and cryoglobulinemic patients, between O.D. values and IgM concentration in rheumatic patients only; a negative correlation has been found in rheumatic patients with regard to C4. The analytical results are, finally, discusses in relation to the reliability of the method as routine test for the detection of circulating IC.