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What Is the Rheumatoid Factor Test?

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Doctors often give people the rheumatoid factor blood test to help diagnose rheumatoid arthritis (RA). It measures rheumatoid factor, an immune system chemical that’s in the blood of many, but not all, people with RA.

Keep in mind that by itself, this test does not show whether you have RA.

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 infections such as hepatitis and mononucleosis. People with cancer may also have it.

Some healthy people can have rheumatoid factor, too. And some people with RA don’t have it. That’s why this test will not, by itself, show whether you have rheumatoid arthritis.

WebMD Medical Reference

Reviewed by David Zelman, MD on February 11, 2014
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