[Circulating immune complexes: optimization and characteristics of the C1q(I125) fixation test].

The present paper describes the optimisation of a liquid phase [125I] C1q binding assay for the detection of circulating immune complexes. Blood must be collected without any anticoagulant. The serum can be stored or transported as usual without damage. A 90 min incubation is needed to reach the equilibrium of the reaction; polyethylene glycol (2,5% final concentration) is added to precipitate the [125I] C1q-CIC complex. By its simplicity and reproducibility, this test can be currently employed, especially in the case of treatment by plasmapheresis.