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    What Is the Rheumatoid Factor Test?

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    Doctors often use the rheumatoid factorblood test to help diagnose rheumatoid arthritis (RA). It measures rheumatoid factor, an immune system substance present in many, but not all, people with RA.

    Keep in mind that by itself, this test does not show whether you have RA. The most important factor in making the diagnosis is an examination by the doctor that reveals the presence of objective arthritis.

    How is the test done?

    It’s quick and almost painless. Your doctor will use a needle to collect blood from a vein, and then send your blood sample to a lab for testing.

    Your doctor may also order other lab tests, X-rays, an MRI, ultrasound, and other scans to check on your symptoms.

    Do I need to do anything to prepare for it?

    No. Some people are more sensitive than others about having blood taken. If you have questions, talk to your doctor before the test. If you feel faint or nauseated, let someone know.

    What do the results mean?

    They give your doctor more information to consider, along with your physical exam, other tests, and your history of symptoms.

    The results may also help predict how your condition will go. If you have RA and high levels rheumatoid factor, your disease may be more aggressive.

    Is rheumatoid factor only found in people with RA?

    No. People with other immune system conditions, such as lupus and Sjogren's syndrome, can also have it. So can people with chronic infections such as viral hepatitis and even some healthy people. Thus, other factors need to be considered when looking at a positive result for rheumatoid factor.  

    WebMD Medical Reference

    Reviewed by David Zelman, MD on February 19, 2016
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