What test is primarily used to detect circulating immune complexes in serum for autoimmune diseases such as rheumatoid arthritis?

The assay of cryoglobulins is employed to detect circulating immune complexes in serum, particularly in the context of autoimmune diseases such as rheumatoid arthritis. Circulating immune complexes consist of antibodies bound to antigens, and their presence can indicate immune system dysfunction often observed in autoimmune conditions. These complexes may precipitate in the serum at lower temperatures, leading to a condition known as cryoglobulinemia.

In the context of rheumatoid arthritis, the identification of cryoglobulins provides critical insight into the activity of the disease and the associated immune response. As the presence of these complexes can cause various complications, their detection is a valuable diagnostic marker in managing autoimmune diseases.

While other tests listed, such as direct immunofluorescence and enzyme immunoassays, are important tools in immunological diagnostics, they serve different primary purposes. Direct immunofluorescence is mainly utilized for identifying specific antigens or antibodies in tissues, and enzyme immunoassays are typically used for measuring concentrations of specific antibodies or antigens in serum rather than immune complexes directly. The indirect antiglobulin test is primarily used to detect antibodies against red blood cells and is not specific for the detection of circulating immune complexes. Thus, the assay of cryoglobulins stands