Rheumatoid factor

Rheumatoid factor

Rheumatoid factor (RF or RhF) is an autoantibody (antibody direct against an organism's own tissues) most relevant in rheumatoid arthritis. It is an antibody against the Fc portion of IgG, which is itself an antibody. RF and IgG join to form immune complexes which contribute to the disease process. Not all people with rheumatoid arthritis have detectable rheumatoid factor. Those who do not are said to be "seronegative".

Rheumatoid factor can also be a cryoglobulin (antibody that precipitates on cooling of a blood sample); it can be either type 2 (monoclonal IgM to polyclonal IgG) or 3 (polyclonal IgM to polyclonal IgG) cryoglobulin.

Indications

RF is often determined in patients suspected in any form of arthritis. It has relatively little use there, as 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 be diagnostic and prognostic. It is part of the disease criteria of RA.

Interpretation

High levels RF (generally above 20 IU/mL, 1:40 or over the 95th percentile there is some variation among labs) are indicative of rheumatoid arthritis (present in 80%) and Sjögren's syndrome (present in almost 100%). The higher the levels of RF the higher the possibility of a more destructive articular disease.

There is a high rate of false positives due to other causes, or when other autoimmune diseases may be present. These include: chronic hepatitis, any chronic viral infection, leukemia, dermatomyositis, infectious mononucleosis, scleroderma and systemic lupus erythematosus (SLE).

History

The test was first developed by Dr Eric Waaler in 1940 and developed by Dr H.M. Rose and colleagues. It is therefore still occasionally referred to as the Rose-Waaler or Waaler-Rose test.

References

External links

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