Rheumatoid Factor IgM

Rheumatoid factors are immunoglobulins with antibody activity directed against antigenic sites in the Fc portion of IgG molecules. The main diagnostic value of RF measurement is in the differentiation of Rheumatoid Arthritis (RA), where most patients exhibit the autoantibody, from other joint diseases where RF is rarely present. Patients with rheumatoid arthritis having high levels of rheumatoid factor generally have poorer prognosis, more severe progressive disease with greater joint and bone destruction and higher incidence of nodules and multisystem involvement. Rheumatoid factor levels are generally reasonably constant in individual patients although during a long period of remission some reduction can occur. Rheumatoid factor is sometimes detected in other diseases such as Systemic Lupus Erythematosus (SLE), hepatitis, liver cirrhosis, syphilis and bacterial endocarditis. Sera from rheumatoid arthritis patients most commonly contain IgM RF, but IgG RF and IgA RF also occur. Each class may be present exclusively or in association with one or both of the other isotypes. Rheumatoid Factors are found in 1 to 4 % of the general population. Patients with RA having high levels of RF generally have poorer prognosis, more severe progressive disease with greater joint and bone destruction and higher incidence of nodules and multisystem involvement. The clinical correlation of an elevated RF should be interpreted cautiously. Increased titres may accompany a variety of acute immune responses, particularly viral infections and a number of other diseases (e.g. infectious mononucleosis, tuberculosis, leprosy and liver disease).