Rheumatoid factor (RF)
Rheumatoid factor (RF) is a blood test that measures the amount of the RF antibody in the blood.
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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.
- 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.
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How to Prepare for the Test
You do not need to take special steps before this test.
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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.
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Why the Test is Performed
This test is most often used to help diagnose rheumatoid arthritis or Sjögren syndrome.
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Normal Results
Results are usually reported in one of two ways:
- Value, normal less than 15 IU/mL
- Titer, normal less than 1:80 (1 to 80)
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.
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What Abnormal Results Mean
An abnormal result means the test is positive, which means a higher level of RF has been detected in your blood.
- Many people with rheumatoid arthritis or Sjögren syndrome have positive RF tests.
- The higher the level, the more likely one of these conditions is present. There are also other tests that can be done to help make the diagnosis.
- Not everyone with a higher level of RF has rheumatoid arthritis or Sjögren syndrome.
Your provider should also do another blood test (anti-cyclic citrullinated peptide antibody or anti-CCP antibody), to help diagnose rheumatoid arthritis (RA). Anti-CCP antibody is more specific for RA than RF. A positive test for CCP antibody means RA is probably the correct diagnosis.
People with the following diseases may also have higher levels of RF:
- Hepatitis C
- Systemic lupus erythematosus
- Dermatomyositis and polymyositis
- Sarcoidosis
- Mixed cryoglobulinemia
- Mixed connective tissue disease
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:
- AIDS, hepatitis, influenza, infectious mononucleosis, and other viral infections
- Certain kidney diseases
- Endocarditis, tuberculosis, and other bacterial infections
- Parasite infections
- Leukemia, multiple myeloma, and other cancers
- Chronic lung disease
- Chronic liver disease
In some cases, people who are healthy and have no other medical problem will have a higher-than-normal RF level.
References
Aletaha D, Neogi T, Silman AJ, et al. 2010 Rheumatoid arthritis classification criteria: an American College of Rheumatology/European League Against Rheumatism collaborative initiative. Ann Rheum Dis. 2010;69(9):1580-1588. PMID: 20699241 pubmed.ncbi.nlm.nih.gov/20699241/.
Darrah E, Rosen A, Andrade F. Autoantibodies in rheumatoid arthritis. In: Firestein GS, Budd RC, Gabriel SE, Koretzky GA, McInnes IB, O'Dell JR, eds. Firestein & Kelley's Textbook of Rheumatology. 11th ed. Philadelphia, PA: Elsevier; 2021:chap 59.
Sieghart D, Trouw L, Steiner G. Autoantibodies in rheumatoid arthritis. In: Hochberg MC, Gravallese EM, Smolen JS, van der Heijde D, Weinblatt ME, Weisman MH, eds. Rheumatology. 8th ed. Philadelphia, PA: Elsevier; 2023:chap 96.
Mason JC. Rheumatic diseases and the cardiovascular system. In: Libby P, Bonow RO, Mann DL, Tomaselli GF, Bhatt DL, Solomon SD, eds. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine. 12th ed. Philadelphia, PA: Elsevier; 2022:chap 97.
Pisetsky DS. Laboratory testing in the rheumatic diseases. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 242.