Rheumatoid factor (RF)
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 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.
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.
Why the Test is Performed
Results are usually reported in one of two ways:
If the result is above the normal level, it is positive. A low number (negative result) most often means you do not have rheumatoid arthritis or Sjögren syndrome. However, some people who do have these conditions still have a negative 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.
What Abnormal Results Mean
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.
Andrade F, Darrah E, Rosen A. Autoantibiodies in rheumatoid arthritis. In: Firestein GS, Budd RC, Gabriel SE, McInnes IB, O'Dell JR, eds. Kelley and Firestein's Textbook of Rheumatology. 10th ed. Philadelphia, PA: Elsevier; 2017:chap 56.
Chernecky CC, Berger BJ. Rheumatoid Factor (RF) - blood. In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures. 6th ed. St Louis, MO: Elsevier Saunders; 2013:985-986.
Hoffmann M, Lundberg K, Steiner G. Autoantibodies in rheumatoid arthritis. In: Hochberg MC, Silman AJ, Smolen JS, Weinblatt ME, Weisman MH, eds. Rheumatology. 6th ed. Philadelphia, PA: Elsevier Mosby; 2015:chap 91.
Mason JC. Rheumatic diseases and the cardiovascular system. In: Mann DL, Zipes DP, Libby P, Bonow RO, Braunwald E, eds. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine. 10th ed. Philadelphia, PA: Elsevier Saunders; 2015:chap 84.
Pisetsky DS. Laboratory testing in the rheumatic diseases. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 257.
Review Date: 4/24/2017
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, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
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