Rheumatoid factor is an autoantibody against FC fragments of degenerated IgG molecules and can be classified into four types according to immunoglobulin type: IgM, IgG, IgA and IgE. Rheumatoid factor reacts not only with denatured IgG molecules, but also with its own IgG or allogeneic IgG molecules, and cross-reacts with other antigens and nuclear proteins. Rheumatoid factor is produced in peripheral lymph nodes, synovial membrane, tonsillar lymphoid follicles and bone marrow. Rheumatoid factor has a positive rate of about 80% in rheumatoid arthritis and is one of the important serological markers for the diagnosis of rheumatoid arthritis, but is not the only criterion. And rheumatoid factor is not a specific antibody unique to rheumatoid arthritis. It can be found in a variety of diseases, including autoimmune diseases such as dry syndrome, systemic lupus erythematosus, scleroderma, polymyositis, dermatomyositis, infectious diseases such as bacterial endocarditis, tuberculosis, leprosy, and hematologic diseases. Rheumatoid factor is often used clinically as a differentiating criterion for seronegative spondyloarthropathies. The above questions are for reference only, please refer to the doctor’s face-to-face guidance for specific medication and treatment.