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#### Clinical QuestionShould GPs use anti-citrullinated peptide antibody testing instead of rheumatoid factor for diagnosing rheumatoid arthritis?Early diagnosis and treatment of rheumatoid arthritis (RA) is important in preventing long-term damage and disability. RA should be suspected largely on the basis of clinical findings, such as persistent joint pain, swelling, and stiffness. Further investigations, particularly in primary care, may contribute to the diagnosis. Rheumatoid factor (RF) is an autoantibody associated with RA and its presence has traditionally been used to support the diagnosis. However, RF has a low specificity in primary care and cannot be used to rule in or rule out disease. In contrast, anti-citrullinated peptide antibody (ACPA) has emerged as an alternative serological test, as it has greater specificity and may be preferable to RF in the diagnosis of RA.1 However, it is not yet generally available in primary care.RFs are autoantibodies directed against the Fc region of immunoglobulin IgG. RA is associated with the presence of RF in many, but not all cases. Raised levels are also found in other autoimmune diseases, for example, Sjogren’s syndrome and type 2 cryoglobulinaemia, in infection, and in healthy individuals. ACPAs, also called anti-cyclic citrullinated peptide (anti-CCP) antibodies, are reactive to the amino acid citrulline and are also present in the sera of patients with RA.2 The ACPA test is a laboratory-based enzyme-linked immunosorbent assay (ELISA). Point-of-care testing devices for both RF and ACPA are currently being developed.RA is a destructive inflammatory joint disease with an estimated UK prevalence of 1.2% in females and 0.4% …

Autoimmune markers for the diagnosis of rheumatoid arthritis in primary care: primary care diagnostic technology update