Autoantibodies in the autoimmune rheumatic diseases

The detection of autoantibodies to a variety of antigenic targets plays an important role in the diagnosis of autoimmune rheumatic disease. Rheumatoid factor (RF), antinuclear antibodies (ANA) and anti-neutrophil cytoplasmic antibodies (ANCA) have been key in the diagnosis of rheumatoid arthritis, systemic lupus erythematosus and systemic vasculitis for many years. Antibodies against cyclic citrullinated peptides (ACPA) are more specific than rheumatoid factor for rheumatoid arthritis. Dual positivity for ACPA and RF is strongly predictive of erosive rheumatoid arthritis. Screening for ANA and ANCA should not be undertaken routinely as the specificity of these tests is poor in this setting and low concentrations/titres of RF, ANA and ANCA are common in the well elderly. Repetition of a negative ANA is not likely to be helpful unless there has been a change in symptoms. Rising concentrations/titres of anti-dsDNA and ANCA (proteinase 3 and myeloperoxidase) indicate possible disease relapse, but should not be used as the sole reason for a change in therapy in the absence of clinical features of relapse.