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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
A blood sample is needed. For information on how this is done, see: Venipuncture
How to Prepare for the Test
No special preparation is usually necessary.
How the Test Will Feel
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.
Why the Test is Performed
This test is most often used to diagnose rheumatoid arthritis or Sjogren syndrome.
It may also be used to rule out or diagnose other inflammation-related conditions.
Normal Results
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, and almost all patients with Sjogren syndrome have positive RF tests.
- The higher the level, the more likely one of these conditions is present.There are also other confirmatory tests for these disorders.
- However, not everyone with higher levels of rheumatoid factor has rheumatoid arthritis or Sjogren syndrome.
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.:
- 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
Sometimes, people who are healthy and have no other medical problem will have a higher-than-normal RF level.
Risks
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:
- Excessive bleeding
- Fainting or feeling light-headed
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
References
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.
Reviewed By: Ariel D. Teitel, M.D., M.B.A., Chief, Division of Rheumatology, St. Vincent’s Hospital, New York, NY. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
