Rheumatoid arthritis (RA) is an autoimmune erosive inflammatory arthritis of unknown aetiology. The triggering event is unclear, but blood markers suggesting autoimmune activation include high inflammatory markers and positive antibodies such as rheumatoid factor (RF). RF is positive in around 50–80 % of patients with RA depending on the stage of the disease, but the disease may also be “seronegative”, i.e. negative RF, particularly in early disease. More specific autoantibodies have been described and the anti-citrullinated peptide antibodies (AntiCCP or ACPA) are in routine clinical use currently.