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.
- 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
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
This test is most often used to help diagnose rheumatoid arthritis or Sjögren syndrome.
Rheumatoid arthritis
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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.
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 high level of RF:
- Hepatitis C
- Systemic lupus erythematosus
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- Mixed cryoglobulinemia
- Mixed connective tissue disease
Higher-than-normal levels of RF may be seen in people with other medical problems. However, these high 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.
Reviewed By
Diane M. Horowitz, MD, Rheumatology and Internal Medicine, Northwell Health, Great Neck, NY. Review provided by VeriMed Healthcare Network. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
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, McInnes IB, Koretzky GA, Mikuls TR, Neogi T, O'Dell JR, eds. Firestein & Kelley's Textbook of Rheumatology. 12th ed. Philadelphia, PA: Elsevier; 2025:chap 56.
Deane KD, Pisetsky DS. Laboratory testing in the rheumatic diseases. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 237.
Von Mühlen CA, Chan EKL, Ceribelli A, Fritzler MJ. Clinical and laboratory evaluation of systemic autoimmune rheumatic diseases. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 53.
