INDIVIDUAL TEST 890

C1q antibodies

Indication

Suspected Hypocomplementemic urticarial vasculitis syndrome or SLE with renal involvement.

Method

ELISA

Answer

The result is given as negative or positive.

Reference range

<26 E/mL

Interpretation

C1q antibodies have primary been studied in systemic lupus erythematosus (SLE) and Hypocomplementemic urticarial vasculitis syndrome (HUVS), a SLE-like disease. The presence of C1q antibodies in SLE is 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 decreases 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 Hypocomplementemic urticarial vasculitis syndrome have C1q antibodies. Hypocomplementemic urticarial vasculitis syndrome is almost always characterized by persistence of the C1q antibodies as well as low C1q levels for a long time. C1q antibodies have also been reported in, among other things, membrane proliferative glomerulonephritis and rheumatoid arthritis with vasculitis, conditions with normal C1q content. In SLE, C1q antibodies usually occur in combination with antibodies against native DNA.

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, hypocomplementemia and dsDNA antibodies. The presence of autoantibodies in healthy individuals increases with age.