Positive Rheumatoid Factor

The RF is an antibody detectable in the blood in about 70 percent of persons with rheumatoid arthritis but can often be found in other people as well. In fact, healthy people with no arthritis and no medical problems at all make tiny amounts of this antibody. In 90-95 percent of young, healthy persons, the amount of RF present in the blood is so low that it is considered absent from the blood and the test is considered negative (the "normal" result).

The number of healthy people having a positive RF rises somewhat with age, although sicker elderly people tend to have a positive RF more often than the healthy elderly. Also, when the RF is positive without disease present, it is usually only slightly positive, while higher levels are more likely to indicate "true" disease of one sort or another. See below for conditions other than rheumatoid arthritis associated with a positive RF.

Other conditions associated with arthritis may result in a positive rheumatoid factor: Sjogren's syndrome and systemic lupus erythematosus are good examples, but these conditions usually cause other symptoms and blood test abnormalities that provide clues to the diagnosis.

Certain infections, including endocarditis, viral infections, and others may trigger RF production by the body's immune system. Once the infection passes, repeat RF testing usually reveals negative results. Hepatitis C, a viral infection of the liver, is one of the more common ones, especially when a protein called "cryoglobulin" is present. This infection can be chronic (long-standing) so the RF may remain positive.

Three other situationsdeserve mention:

• People who tend to make one "autoantibody" (an antibody created against a part of one's own organs or tissues) may make others; so if you have an "autoimmune" condition, such as certain thyroid diseases or even type 1 diabetes, you may be more likely to make RF even without an associated disease.

• People with a family history of rheumatoid arthritis (or other RF-associated disorder) are more likely to have relatives with a positive RF, even if no disease is present.

• People "destined" to develop rheumatoid arthritis may have a positive RF detected years before they develop symptoms or signs of the disease. However, of all people with a positive RF and no joint symptoms, the vast majority are thought to remain free of RF-associated disease over time.

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