Rheumatoid factor (RF or RhF) is a blood test performed in patients with suspected rheumatoid arthritis (RA). It is an antibody against the Fc portion of IgG, which is itself an antibody, IgM or IgA type; RF and IgG form immune complexes, which are part of the disease process of various rheumatological diseases. Rheumatoid factor can be either Type 2 (monoclonal IgM to polyclonal IgG) or 3 (polyclonal IgM to polyclonal IgG) cryoglobulin.