Laboratory testing for systemic autoimmune diseases

Abstract

The detection of autoantibodies is well established in daily clinical practice for evaluation of systemic autoimmune diseases like rheumatoid arthritis (RA), connective tissue diseases and vasculitides. Rheumatoid factor (RF) or the anti-citrullinated protein antibody (ACPA) is only observed in approximately 80% of patients suffering from rheumatoid arthritis. Anti-CarP autoantibodies might serve as a novel marker, filling this gap. The detection of anti-nuclear antibody (ANA) facilitates the diagnosis of connective tissue diseases. Elevated levels of anti-centromer antibodies, anti-topoisomerase I [anti-Scl-70] antibodies and the anti-RNA polymerase III antibodies, which belong to the group of ANA, are frequently present in the serum of patients suffering from systemic sclerosis and are therefore incorporated into the new classification criteria. To establish the diagnosis of an antiphospholipid syndrome, the detection of the lupus anticoagulant and the aCL-/anti-β2GPI-antibodies of IgG, IgM and IgA isotypes plays a pivotal role. The antineutrophil cytoplasmic antibodies (ANCAs) are associated with vasculitides of small vessels. Screening with immunofluorescence testing (IFT) is established as the first step followed by additional immunoassays specific for proteinase 3 (PR3) and myeloperoxidase (MPO) autoantibodies. Novel bedside test procedures for these antibodies allow an early diagnosis in critically ill patients. New biomarkers for polymyalgia rheumatic and for spondyloarthritides are also described, but their clinical relevance remains uncertain and necessitates further studies.