Serological testing in small vessel vasculitis.

Serological analysis has a central role in the diagnostic work-up of patients with suspected small vessel vasculitis, both for establishing a specific diagnosis and for the monitoring of response to therapy. Autoantibodies can be detected in all forms of primary small vessel vasculitis as well as in the most common forms of secondary vasculitis. For primary vasculitis the most important serological test is for ANCA. ANCA can be found in 75-95% of patients with pauci-immune small vessel vasculitis leading to this subgroup of vasculitides being named ANCA associated vasculitis. ANCA levels often follow this disease course, but the value of serial ANCA testing is controversial. Other important autoantibodies in primary small vessel vasculitis are anti-glomerular basement membrane antibodies, anti-C1q, anti-galactose deficient IgA and cryoglobulins. A wide variety of systemic inflammatory diseases and infections can be complicated by small vessel vasculitis and detected by serological testing. Important examples are SLE, rheumatoid arthritis, Hepatitis C and HIV.