Investigations in systemic vasculitis. The role of the laboratory

The diagnosis of systemic vasculitis is challenging. Laboratory testing may provide useful information. Routine laboratory tests include erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), blood count, serum creatinine, urinalysis, specific autoantibodies, complement, immunoglobulin, cryoglobulin, and Hepatitis B and C serology. Although ESR and CRP are often helpful for the diagnosis of vasculitis, they are nonspecific and do not help in distinguishing between vasculitis disease activity and a concomitant infection or another source of inflammation. A few autoantibodies are helpful for diagnosis, such as anti-neutrophil cytoplasmic antibodies (ANCAs) (in ANCA-associated small-vessel vasculitis), anti-glomerular basement membrane (GBM) antibodies (in anti-GBM antibody disease), and anti-C1q antibodies (in immune complex-associated small-vessel vasculitis). The 2017 revised consensus recommendations on ANCA testing state that high-quality antigen-specific immunoassays are the preferred screening methodology for the diagnosis of ANCA-associated vasculitis. ANCA subtypes (proteinase-3-ANCA and myeloperoxidase-ANCA) are associated with different epidemiological, genetic, and clinical features.