Rheumatoid Factor

The rheumatoid factor blood test helps to diagnose rheumatoid arthritis.

• Rheumatoid factor is an antibody that is detectable in the blood of approximately 80% of adults with rheumatoid arthritis.
• Rheumatoid factor test is used by health care professionals to help in diagnosing rheumatoid arthritis.
• Sometimes rheumatoid factor can be detected in the blood of normal individuals and of those with other autoimmune diseases that are not rheumatoid arthritis.
• In people with rheumatoid arthritis, high levels of rheumatoid factor can indicate a tendency toward more aggressive disease and/or a tendency to develop rheumatoid nodules and/or rheumatoid lung disease.

Rheumatoid factor is an antibody that is measurable in the blood with a routine blood test. Rheumatoid factor is actually an antibody that can bind to other antibodies. Antibodies are normal proteins in our blood that are important parts of our immune system. Rheumatoid factor is an antibody that is not usually present in the normal individual. Because rheumatoid factor antibody binds to normal antibodies, it can be generally referred to as an autoantibody. Health care professionals use the rheumatoid factor test to assist in the diagnosis of rheumatoid arthritis.

Rheumatoid factor is sometimes abbreviated as "RF."

Most commonly, rheumatoid factor is 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) with rheumatoid arthritis.

The "normal" range (or negative test result) for rheumatoid factor is less than 14 IU/ml. Any result with values 14 IU/ml or above is considered abnormally high, elevated, or positive.

High levels of rheumatoid factor (rheumatoid factor "positive") are associated with a tendency toward 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.

Yes. Rheumatoid factor is also present in patients with other conditions, including other connective tissue diseases (such as systemic lupus erythematosus and Sjögren's syndrome), 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. This occurs more frequently in people with family members who have rheumatoid arthritis. So precise interpretation of rheumatoid factors requires a complete knowledge of the patient's history and medical status.