Rheumatoid factor (RF) is an autoantibody, meaning it is produced by the immune system and directed against the body's own proteins. Specifically, RF targets the Fc portion of immunoglobulin G (IgG), forming immune complexes that can contribute to inflammation. It is most strongly associated with rheumatoid arthritis (RA) but is not exclusive to it.
Testing for RF is part of the standard workup when symptoms suggest an autoimmune rheumatic condition. Persistent joint pain, swelling (particularly in the small joints of the hands and feet), prolonged morning stiffness lasting more than 30 minutes, and unexplained fatigue are the typical triggers for investigation. RF is usually ordered alongside anti-CCP antibodies, CRP, ESR, and a full blood count to build a clearer picture.
A positive RF result supports a diagnosis of rheumatoid arthritis when combined with the right clinical features, but it does not confirm it on its own. RF can also be elevated in Sjogren's syndrome, systemic lupus erythematosus, chronic infections (such as hepatitis C and tuberculosis), and certain liver conditions. It can even be positive in a small percentage of healthy people, particularly older adults. This is why clinical context matters so much in interpreting the result.
Equally important is the fact that a negative RF does not rule out rheumatoid arthritis. Around 20 to 30 percent of people with RA are seronegative, meaning their RF is negative despite having active disease. Anti-CCP antibodies tend to be more specific for RA and are often checked alongside RF. If anti-CCP is positive and RF is negative, the clinical picture still points toward RA. Your GP or rheumatologist will assess the result in the context of your symptoms, physical examination, and other investigations.
This test is used when symptoms suggest an autoimmune rheumatic condition — particularly persistent joint pain, swelling, stiffness, or fatigue. It forms part of the standard workup for suspected rheumatoid arthritis, often alongside anti-CCP antibodies, CRP, ESR, and a full blood count.
