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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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