Rheumatoid factor (RF) is a blood test that measures the amount of the RF antibody in the blood.
Most of the time, blood is drawn from a vein located on the inside of the elbow or the back of the hand.
In infants or young children, a sharp tool called a lancet may be used to puncture the skin.
Most of the time, you do not need to take special steps before this test.
You may feel slight pain or a sting when the needle is inserted. You may also feel some throbbing at the site after the blood is drawn.
This test is most often used to help diagnose rheumatoid arthritis or Sjögren syndrome.
Results are usually reported in 1 of 2 ways:
A low number (normal result) most often means you do not have rheumatoid arthritis or Sjögren syndrome. However, some people who do have these conditions still have a "normal" or low RF.
Normal value ranges may vary slightly among different laboratories. Talk to your health care provider about the meaning of your specific test results.
An abnormal result means the test is positive, which means a higher level of rheumatoid factor has been detected in your blood.
Your provider may do another blood test (anti-CCP antibody), to help diagnose rheumatoid arthritis.
People with the following diseases may also have higher levels of RF:
Higher-than-normal levels of RF may be seen in people with other medical problems. However, these higher RF levels cannot be used to diagnose these other conditions:
In some cases, people who are healthy and have no other medical problem will have a higher-than-normal RF level.
Reviewed By: Gordon A. Starkebaum, MD, Professor of Medicine, Division of Rheumatology, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.