RF is an autoantibody directed against the Fc portion of immunoglobulin G (IgG). The most clinically measured and useful class of rheumatoid factor is IgM, which is found in 50-90 % of patients with rheumatoid arthritis. It is also seen in Sjögren’s syndrome (70-80 %) and to a lesser degree in other rheumatological conditions, such as SLE, systemic sclerosis, juvenile rheumatoid arthritis and polymyositis. It is seen in 5-10 % of healthy adults and also in those with an intercurrent infection (up to 50 %).
Arthralgia, bone pain Differential diagnosis of arthritis
SST (gold top)
5-10 mL (1 mL serum)