Rheumatoid Factor (RF)

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Rheumatoid factor (RF) facts

  • Rheumatoid factor is an antibody that is detectable in the blood of approximately 80% of adults with 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 Arthritis (RA) Pictures Slideshow

What is rheumatoid factor?

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. Rheumatoid factor is sometimes abbreviated as "RF."

What is the normal range for rheumatoid factor?

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.

For what is the rheumatoid factor test used?

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.

Medically Reviewed by a Doctor on 2/2/2016

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Picture of a joint capsule with RA

What Is Rheumatoid Arthritis (RA)?

Rheumatoid arthritis (RA) is an autoimmune disease that causes chronic inflammation of the joints. Autoimmune diseases are illnesses that occur when the body's tissues are mistakenly attacked by their own immune system. The immune system contains a complex organization of cells and antibodies designed normally to "seek and destroy" invaders of the body, particularly infections.