Rheumatoid factor (RF) is a blood test that measures the amount of the RF antibody in the blood.
A blood sample is needed. For information on how this is done, see: Venipuncture
No special preparation is usually necessary.
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
It may also be used to rule out or diagnose other inflammation-related conditions.
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.
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.:
Sometimes, people who are healthy and have no other medical problem will have a higher-than-normal RF level.
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
Goodyear CS, Tighe H, McInnes IB. Rheumatoid factors and other autoantibodies in rheumatoid arthritis. In: Firestein GS, Budd RC, Harris Jr. ED, McInnes IB, Ruddy S, eds. Kelley's Textbook of Rheumatology. 8th ed. Philadelphia, Pa: W.B. Saunders Company;2008:chap 51.