Rheumatoid factor


Rheumatoid factor is the autoantibody that was first found in rheumatoid arthritis. It is defined as an antibody against the Fc portion of IgG and different RFs can recognize different parts of the IgG-Fc. RF and IgG join to form immune complexes that contribute to the disease process.
Rheumatoid factor can also be a cryoglobulin ; it can be either type 2 or type 3 cryoglobulin.
Although predominantly encountered as IgM, rheumatoid factor can be of any isotype of immunoglobulins, i.e. IgA, IgG, IgM, IgE, IgD.

Testing

RF is often evaluated in patients suspected of having any form of arthritis even though positive results can be due to other causes, and negative results do not rule out disease. But, in combination with signs and symptoms, it can play a role in both diagnosis and disease prognosis. It is part of the usual disease criteria of rheumatoid arthritis.
The presence of rheumatoid factor in serum can also indicate the occurrence of suspected autoimmune activity unrelated to rheumatoid arthritis, such as that associated with tissue or organ rejection. In such instances, RF may serve as one of several serological markers for autoimmunity. The sensitivity of RF for established rheumatoid arthritis is only 60-70% with a specificity of 78%.

Interpretation

High levels of rheumatoid factor occur in rheumatoid arthritis and Sjögren's syndrome. The higher the level of RF the greater the probability of destructive articular disease. It is also found in Epstein–Barr virus or Parvovirus infection and in 5 to 10% of healthy persons, especially the elderly.
There is an association between rheumatoid factor and more persistently active synovitis, more joint damage, greater eventual disability and arthritis.
Other than in rheumatoid arthritis, rheumatoid factor may also be elevated in:
The test was first described by Norwegian Dr Erik Waaler in 1940 and redescribed by Dr Harry M. Rose and colleagues in 1948. Redescription is said to be due to the uncertainties due to World War II. It is still referred to as the Waaler-Rose test.