• An antibody found in about 85% of people with rheumatoid arthritis; also appears in other diseases and sometimes in healthy people.
  Harvard Dictionary of Health Terms
  Harvard Medical Publishing, 2011
• Antibodies directed against antigenic determinants in the Fc region of IgG, frequently found in the serum of patients with rheumatoid arthritis and other connective tissue diseases.
  CRISP Thesaurus
  National Institutes of Health, 2006
• Autoantibodies found in adult RHEUMATOID ARTHRITIS patients that are directed against GAMMA-CHAIN IMMUNOGLOBULINS.
  NLM Medical Subject Headings
  U.S. National Library of Medicine, 2025
• Antibodies in the serum of individuals with rheumatoid arthritis that react with antigenic determinants or immunoglobulins that enhance agglutination of suspended particles coated with pooled human gamma-globulin. Rheumatoid factors also occur in other autoimmune and certain infectious diseases.
  NCI
  U.S. National Cancer Institute, 2021
• Antibodies that bind other immunoglobulins frequently seen in rheumatoid arthritis but can be found in other autoimmune diseases.
  NICHD Pediatric Terminology
  U.S. National Cancer Institute, 2021
• Antibodies directed against the Fc fragment of immunoglobulin G (IgG) are called rheumatoid factors (RFs). They are heterogenous and usually composed of immunoglobulin M (IgM).
  Medscape
  WebMD, 2025
• A rheumatoid factor test measures the amount of rheumatoid factor in your blood. Rheumatoid factors are proteins produced by your immune system that can attack healthy tissue in your body.
  Mayo Clinic
  Mayo Foundation for Medical Education and Research, 2025