What is Factor, Rheumatoid?

Antibodies directed against antigenic determinants, i.e., Gm (gamma chain), in the Fc region of IMMUNOGLOBULIN G, found in the serum of about 80% of patients with classical or definite rheumatoid arthritis, but in only about 20% of patients with juvenile rheumatoid arthritis. Rheumatoid factors may be IMMUNOGLOBULIN M, IMMUNOGLOBULIN G, or IMMUNOGLOBULIN A antibodies, although other serological tests measure only IMMUNOGLOBULIN M. Rheumatoid factors also occur in other connective tissue diseases and infectious diseases. (From Dorland, 28th ed)