RF has a sensitivity of 70% and specificity of 70% for rheumatoid arthritis (RA)
RF is present in 50% with early RA, and 80% with established disease
What is RF?
RF refers to a family of antibodies directed against the Fc portion of IgG (the Fc molecule is essential for complement fixation and interaction with the Fc receptor, and thus for uptake of immune complexes)
High-affinity IgM-RF, as well as IgG and IgA subtypes, are commonly found in RA (note that approximately 30% of RA patients are negative for RF)
High-titer IgM- and IgA-RF are associated with increased bone erosion, more rapid disease progression, worse outcome, and extra-articular manifestations
Other conditions associated with RF
RF is not specific to RA
A transient increase of IgM-RF is part of the normal immunoregulatory process during a bacterial or viral infection, and therefore low-titer IgM-RF can be found in 10-15% of healthy individuals.
IgM-RF is also present in high titer in most patients with primary Sjögren’s syndrome or mixed cryoglobulinemia and can be found in all other rheumatic autoimmune diseases, as well as chronic infections.