Rheumatoid factor or RF is an autoantibody directed against the constant region of immunoglobulins. It is used as an aid for the diagnosis of rheumatoid arthritis (RA) and Sjögren’s syndrome. Moreover, presence of RF is an indicator of inflammatory and autoimmune activity.
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 plays a role in diagnosis and disease prognosis of rheumatoid arthritis (RA). It is part of the current ACR criteria for RA classification.
About 75% of those with RA and as many as 60-70% of those with Sjögren´s syndrome will have a positive RF test. However, RF may also be detected in people with a variety of other disorders, such as persistent bacterial, viral, and parasitic infections, and certain cancers. It may sometimes be seen in those with lung disease, liver disease, and kidney disease, and it can be found in a small percentage of healthy people. The frequency of positive RF results occurring in people who do not have RA or Sjögren´s syndrome increases with age.
There are different laboratory methods for measurement of RF, e.g. latex agglutination or Waaler Rose test. Today, the most common is enzyme-linked immunosorbant assay (ELISA).
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