Rheumatoid factors $$$

Autoantibodies against the Fc part of complexed or altered IgG. The rheumatoid factors can belong to all immune classes (IgG, IgM, IgA). The classical rheumatoid factor is an autoantibody of the immune class IgM. The IgM isotypes are predominantly determined.

Standard value: The standard value in serum is < 40 IU/ml

Pathologically increased: in rheumatoid arthritis (80%), lupus erythematosus (often), Sjörgen syndrome, systemic sclerosis, Tbc, syphilis, sarcoidosis, primary biliary cirrhosis, Waldenström's disease, healthy persons, subacute bacterial endocarditis, mononucleosis, acute viral hepatitis, rheumatoid arthritis, type II kyroglobulinemia, parasitic, viral and bacterial infections, vasculitis, chronic lung diseases

• Primary chronic polyarthritis (rheumatoid arthritis) (50-90%)
• subacute bacterial endocarditis (50-60%)
• Lupus erythematosus, systemic (15-35%)
• Sjögren's syndrome (75-95%)
• Cryoglobulinemia (40-100%)
• Mixed Connective Tissue Disease (MTCD) (50-60%)
• Scleroderma (20-30%)
• Polyarteritis nodosa,
• Dermatomyositis about 30%.

Negative for arthropathic psoriasis!

RF should only be assessed in the context of clinical symptoms.

Auto-Ak against citrullinated proteins / peptides(anti-CPA, ACPA) have a higher sensitivity in the diagnosis of RA than the rheumatoid factor!

1. Böhm BO (2018) Autoantibody diagnostics. In: Neumeier B et al. (Eds) Clinical guide to laboratory diagnostics. Elsevier GmbH S. 412-413