Anti-IgG type test to assay circulating immune complexes from polyethylene glycol precipitates compared with C1q binding and Raji cell tests.

Immune complexes (IC) from over 100 normal and patient serum samples were assayed by turbidimetry using anti-IgG as the indicator following a three-step extraction with polyethylene glycol. For 70 patient samples, a high linear correlation was found between the present assay and the C1q-binding test (r = 0.812). Correlation with the Raji cell test was poor (r = 0.176). Both the present test and the Raji cell test showed greater sensitivity for identifying sera with elevated IC levels than the C1q binding test. The present approach may be accomplished using indicators other than turbidimetry, such as light scatter and isotopically-labelled anti-IgG.