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Rheumatoid Factor

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Also known as: RF
Formal name: Rheumatoid Factor

The Test Sample

What is being tested?

Rheumatoid factor (RF) is an autoantibody, an immunoglobulin M (IgM) protein that is produced by the body's immune system. Autoantibodies attack a person's own tissues, mistakenly identifying the tissue as "foreign." While the biologic role of RF is not well understood, its presence is useful as an indicator of inflammatory and autoimmune activity. This test detects and measures RF in the blood.

The RF test is a valuable test for helping to diagnose rheumatoid arthritis (RA). About 80% of those with RA will have a positive RF test. However, RF may also be detected in people with a variety of other disorders, including other autoimmune disorders such as Sjögren syndrome, as well as persistent bacterial, viral, and parasitic infections, and certain cancers. It may sometimes be seen in those with lung disease, liver disease, and kidney disease, and it can be found in a small percentage (1-5%) of healthy people.

How is the sample collected for testing?

A blood sample is collected from a vein in the arm.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.