Rheumatoid factor (RF) is a blood test that measures the amount of the RF antibody in the blood.
Most of the time blood is typically 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.
Results are usually reported in one of two ways:
A low number (normal result) usually means you do not have rheumatoid arthritis or Sjogren syndrome. However, some people who do have these conditions still have a "normal" or low rheumatoid factor (RF).
Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
An abnormal result means the test is positive, which means higher levels of rheumatoid factor have 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 rheumatoid factor:
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.
Andrade F, Darrah E, Rosen A. Autoantibiodies in rheumatoid arthritis. In: Firestein GS, Budd RC, Gabriel SE, et al, eds. Kelley's Textbook of Rheumatology. 9th ed. Philadelphia, Pa: Saunders Elsevier; 2012:chap 56.