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Rheumatoid Factor Test

The rheumatoid factor test is a commonly ordered test to help diagnose rheumatoid arthritis. This test measures rheumatoid factor, which is an antibody in the blood that's present in many people with RA. In fact, the rheumatoid factor blood test is eventually positive in 70% to 80% of people with RA, although in early arthritis the percentage may be smaller. Rheumatoid factor may also be elevated in other autoimmune diseases besides RA. 

How is the rheumatoid factor test done?

This test is quick and virtually painless. Blood is collected from a vein using a needle and the blood sample is sent to a lab for analysis.

Along with rheumatoid factor, your doctor may order other lab tests, including:

  • Complete blood count (CBC) to assess blood cells in the body and evaluate for anemia.
  • Antinuclear antibody (ANA) -- antibodies that might be present in 30% to 40% of people with RA.
  • Erythrocyte Sedimentation rate (SED rate) and C-reactive protein (CRP) -- markers of inflammation.
  • Anti-CCP antibody, which is found in most patients with RA.

Other tests, including X-rays, MRI, ultrasound, and other scans, may be ordered. These tests will help the doctor make an accurate diagnosis.

Are there special preparations for the rheumatoid factor test?

There are no special preparations for a rheumatoid factor test. Some people are more sensitive than others about having blood drawn. If you have any fears or questions, talk to your doctor before the test. If you feel faint or nauseated, be sure to let someone know.

What do the results of the rheumatoid factor test mean?

The rheumatoid factor test may provide your doctor more information to add to the findings of a physical exam, other tests, and your history of symptoms in order to make an accurate diagnosis.

The rheumatoid factor test may also help predict the severity of disease. Studies show that when RA is linked with high levels of rheumatoid factor, it may signify more aggressive disease.

Is rheumatoid factor positive in other ailments?

The rheumatoid factor test may be positive in people who have other autoimmune diseases such as systemic lupus erythematosus (lupus) and Sjogren's syndrome.

Rheumatoid factor can also be positive in people who suffer with infections. These may include hepatitis, mononucleosis, tuberculosis, and syphilis. Patients with cancer and may also test positive for rheumatoid factor.

Remember, positive results from the rheumatoid factor test do not automatically mean you have rheumatoid arthritis. Rheumatoid factor may be positive in some healthy individuals and negative in people who actually have RA.

WebMD Medical Reference

Reviewed by David Zelman, MD on February 11, 2014
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