Rheumatoid Factor

Rheumatoid factor is actually an antibody that can bind to other antibodies, and can be measured in the blood.  Antibodies are normal proteins in our blood that are important parts of our immune system, however Rheumatoid factor is an antibody that is not usually present in the normal individual.


Rheumatoid factor is commonly used as a blood test for the diagnosis of rheumatoid arthritis. Rheumatoid factor is present in about 80% of adults (but a much lower proportion of children)


Rheumatoid factor is also present in patients with other conditions, including other connective tissue diseases (such as systemic lupus erythematosus), some infectious diseases (such as infectious hepatitis, syphilis, infectious mononucleosis, parasites, and tuberculosis), liver disease, and sarcoidosis.  Rheumatoid factor can also sometimes be present in normal individuals without diseases, however this occurs more frequently in people with family members who have rheumatoid arthritis.


High levels of rheumatoid factor are associated with more severe rheumatoid disease. This factor is also associated with a higher tendency to develop non-joint manifestations of rheumatoid disease, such as rheumatoid nodules and rheumatoid lung disease.