Rheumatoid factor (RF)

Rheumatoid factor (RF) is a blood test that measures the amount of the RF antibody in the blood.

Why is the Test 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.

How is the Test Performed?

A blood sample is needed. For information on how this is done, see: Venipuncture

Preparation for the Test

No special preparation is usually necessary.

How will the Test 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.

Rheumatoid factor (RF) 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)

Normal Results for Rheumatoid factor (RF)

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:

• Scleroderma
• Systemic lupus erythematosus
• Adult Still's disease
• Dermatomyositis
• Sarcoidosis

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.

Blood test

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.

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