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Rheumatoid factor (RF) is an antibody that attacks the Fc portion of IgG antibodies and is used as a diagnostic marker for rheumatoid arthritis (RA). Approximately 70–80% of people with RA are RF-positive, but RF also appears in other autoimmune diseases (Sjögren's, lupus), chronic infections, and in up to 10% of healthy older adults. Anti-CCP antibodies are now considered more specific for RA and are increasingly tested alongside RF to improve diagnostic accuracy.
Also known as: Facteur rhumatoïde, Factor reumatoide, RA Factor, RF, Rheumafaktor, Rheumatoid Factor, Romatoid faktör, 류마티스인자
High RF is found in 75% of rheumatoid arthritis cases. It also appears in Sjogren's syndrome, cryoglobulinemia, chronic infections, and in up to 10% of healthy elderly individuals.
Standard positive cutoff is above 14 IU/mL. Optimal is below 14 IU/mL. RF combined with anti-CCP antibodies provides the most accurate RA diagnosis.