Rheumatoid factor is an antibody directed against the Fc portion of the IgG molecule. Polyreactive RF has binding specificity for substances other than IgG like nuclear components. This polyreactive RF is usually of the IgM class with low affinity. RF is not specific only for Rheumatoid arthritis, but it is often seen in cases of chronic infection and other systemic inflammatory conditions. Healthy individuals > 65 years of age may also show positive RF results. In addition to the common IgM RF, both IgA RF & IgG RF have been detected. IgA RF has been related to the more severe form of the disease with erosions.