What is Rheumatoid factor (R.F) ?
• It is an IgM Ab (occasionally IgG, IgA or IgE) which reacts with Fc portion of human IgG, this occurs usually in patients with rheumatoiddisease (70-80% of cases), but is not diagnostic.
• It exists as an (Rh.F. - Ig.G - C) complex in synovial membrane.
So, complement is lowered in synovial fluid and not in the serum.
Methods of detection
1- Latex method (agglutination test)
Ab (Rh. F. in the serum) +
Ag (latex coated with Ig G)
2- Rose waaler test. (agglutination test)
Ab (Rh. F. in the serum) +
Ag (sheep's RBCs coated witl1 anti-erythrocyte antibodies)
Latex is more sensitive, but Rose Waaler is more specific.
Conditions in which Rh. F is +ve
• Autoimmune rheumatic diseases .- Rheumatoid arthritis (70 % - 80 %).
- SLE (15-35 %)
- Polymyositis, dermatomyositis (5-10 %).
- Mixed connective tissue disease (50-60%).
- Sjogren's disease (90 %).
- Scleroderma (30 %).
• Infections
- T. B. - Infective endocarditis.
- Syphilis - Kala - azar
- HCV - HIV
• Normal population
Especially elderly and relatives of patients with rheumatoid arthritis.
• Miscellaneous .
Autoimmune hepatitis. - Fibrosing alveolitis.
Sarcoidosis. - Waldenstroms macroglobulmamia.
Chronic liver disease. - Cryoglobulinemia.