Circulating Immunocomplexes

The detection of immune complexes has not been shown to be essential in any clinical condition but may be helpful in monitoring disease activity in systemic lupus erythematosus (SLE) and may provide useful diagnostic information in two rare syndromes, Lyme arthritis and SLE-related syndrome or other vasculitis.

The serum levels of circulating immunocomplexes (ICs), as measured by immunoassays detecting C1q and C3d, have been shown to be significantly elevated in patients with systemic lupus erythematosus (SLE) and are significantly associated with the clinical and serological disease activities. It could therefore be assumed that simultaneous use of C1q and C3d detection would be useful for CIC quantitative assessment data interpretation and help to explain the nature and pathogenic importance of CIC material detection in individual disease.

A previous WHO collaborative study for the evaluation of 18 methods most frequently used for detection of circulating ICs presented that optimal screening for CICs might be achieved by parallel application of several different methods using reagents of different specificity.

Measurement of CH50 is a useful tool to screen for complement-deficiency associated immunodeficiency and some vasculitides. Significantly reduced or lack of complement components can result in recurrent bacterial infections or sepsis. In such situations, it is necessary to measure CH50 levels together with assays of individual complement components. The sensitivity and specificity of CH50 measurement limits the utility of the test as a widespread screening tool for vasculitis; however, serves as a cost-effective screening method for individuals with specific clinical indications.