rheumatoid factor

Rheumatoid factor (RF or RhF) is an autoantibody (antibody directed 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.^{[citation needed]}

About 80% of 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 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.^[1]

Interpretation

High levels of rheumatoid factor (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%).^[2] The higher the levels of RF the higher the possibility of a more destructive articular disease.^{[citation needed]}

In patients on etanercept or infliximab and DMARDs the levels of rheumatoid factor reduces, which is associated with reduced clinical disease activity.^[2]

Rheumatoid factor may also be elevated in: chronic hepatitis, any chronic viral infection, leukemia, dermatomyositis, infectious mononucleosis, systemic sclerosis and systemic lupus erythematosus (SLE).^{[citation needed]}

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.^[3][4]

References

External links

• MedlinePlus on RF
• Labtestsonline page on RF