Rheumatoid factor (RF)Definition:
Rheumatoid factor (RF) is a blood test that measures the amount of the RF antibody in the blood.
How the test is performed:
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.
- The blood collects in a small glass tube called a pipette, or onto a slide or test strip.
- A bandage is put over the spot to stop any bleeding.
How to prepare for the test:
Most of the time you do not need to take special steps before this test.
How the test will feel:
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:
- Less than 40-60 u/mL
- Less than 1:80 (1 to 80) titer
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.
What abnormal results mean:
An abnormal result means the test is positive, which means higher levels of rheumatoid factor have been detected in your blood.
- Most patients with rheumatoid arthritis or Sjogren syndrome have positive RF tests.
- The higher the level, the more likely one of these conditions is present. There are also other tests for these disorders that help make the diagnosis.
- Not everyone with higher levels of rheumatoid factor has rheumatoid arthritis or Sjogren syndrome.
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.
|Review Date: 4/20/2013|
Reviewed By: Gordon A. Starkebaum, MD, Professor of Medicine, Division of Rheumatology, University of Washington School of Medicine. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, Bethanne Black, Stephanie Slon, and Nissi Wang.
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