C1q antibodies

Indication

Suspected Hypocomplementary urticarial vasculitis or SLE with renal involvement.

Method

ELISA - and the findings of C1q antibodies also supplementing with Western blot - see below!

Response

Primary finding of C1q antibodies is confirmed with an additional analysis by Western blot. A confirmation with a western blot can be used to differentiate between SLE and Hypocomplementary urticarial vasculitis. In SLE C1q antibodies are usually not detected by Western blot (C1q antibodies of SLE type). C1q antibodies in Hypocomplementary urticarial vasculitis generally exhibit a characteristic pattern in Western blot analysis.

Interpretation

C1q antibodies have primary been studied in systemic lupus erythematosus (SLE) and Hypocomplementary urticarial vasculitis, a SLE-like disease. The presence of C1q antibodies in SLE is are associated with severe illness, often with renal involvement. The highest concentrations are associated with disease relapse, when the level of C1q simultaneously is low. High concentration of antibodies usually decrease rapidly in response to treatment. Almost 100% of all SLE patients with renal involvement have C1q antibodies. The prevalence is about 50% for severe SLE without renal involvement. C1q antibodies are rarely detected in mild SLE. Close to 100% of patients with Hypocomplementary urticarial vasculitis have C1q antibodies. Hypocomplementary urticarial vasculitis is almost always characterized by persistence of the C1q antibodies as well as low C1q levels for a long time.

Autoantibodies against C1q have also been detected in patients with Felty's syndrome, Morbus Bechterew, Mixed connective tissue disease (MCTD), Polyarteritis nodosa (PAN), Essential mixed cryoglobulinemia, and Goodpasture's syndrome.

In SLE there is no correlation with disease activity, but the presence of antibodies correlates positively with lupus nephritis, skin lesions, hypocomplementemi and dsDNA antibodies. The presence of autoantibodies in healthy individuals increases with age.

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Packages and other tests

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Clinical studies