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Rheumatoid Factor


Normal Range = Negative (<1:16).

Rheumatoid factor (RF) is an antibody found in the blood of many people with rheumatoid arthritis and is believed to play a role in tissue destruction associated with this disease.

RF is found in the blood of up to 5% of healthy elderly people, and sometimes although much less frequently in the blood of healthy young people.

Several infectious disorders, chronic inflammation, and other diseases may trigger production of RF.

Positive in rheumatoid arthritis (75-90%), Sjogren's (80-90%), scleroderma, dermatomyositis, SLE (30%), sarcoidosis, Waldenstrom's macroglobulinemia. Drugs: methyldopa, others.

Since the blood does not normally contain RF, its presence, along with other characteristic symptoms, helps confirm rheumatoid arthritis and helps distinguish it from rheumatic disorders, such as osteoarthritis, ankylosing spondylitis, psoriatic arthritis, and gout, which are not associated with RF production.

High RF levels are generally found in people with more severe and active disease and may be associated with a worse prognosis.

The presence of RF in a blood sample, particularly in low concentrations, does not provide definitive diagnosis of rheumatoid arthritis because it may also be found in many other diseases, including bacterial endocarditis, malaria, syphilis, tuberculosis, cirrhosis of the liver, hepatitis, and infectious mononucleosis. Moreover, some people produce RF in the absence of any disease, particularly in old age.

Conversely, failure to find RF does not rule out rheumatoid arthritis because up to 20% of people with this disorder produce no RF or have it at very low levels. In particular, young people with juvenile rheumatoid arthritis often have no RF in their blood.




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