Reference Values

Negative

Note: The ability to demonstrate rheumatoid factor (RF) in patients with clinical RA varies from 50-95%, depending primarily on stage of disease. There are 15-20 diseases other than RA which are known to cause positive test results; these include bronchitis, cirrhosis, hepatitis, renal homograft, subacute bacterial endocarditis, syphilis, tuberculosis, and viral disease. “Normal” persons also show a low incidence of RF (2-4%) which increases with age, such that persons over 60 years have a positive test incidence of 5-10%. Because of these factors, it has been estimated that only half of specimens with positive RA tests represent patients with RA.