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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 Values

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.:

Sometimes, people who are healthy and have no other medical problem will have a higher-than-normal RF level.

What the risks are

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.


Review Date: 6/28/2011
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.
The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. © 1997- A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.
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