reumafactor

Rheumatoid factor (RF) is an autoantibody directed against the Fc region of immunoglobulin G (IgG). Most RFs are of the IgM class, but IgA- and IgG-class RF can also occur. RF is a serologic marker used in the evaluation of inflammatory arthritis, but it is not specific to a single disease.

RF is detected by immunoassays such as nephelometry, ELISA, or latex agglutination. Results are reported as a titer or index, with cutoff values varying by assay. The test may be reported as positive or negative, and higher titers can be associated with certain disease features, though interpretation depends on the clinical context.

In rheumatoid arthritis (RA), RF is present in about 70–80% of patients with established disease, but only a subset of patients with early RA. RF positivity alone does not confirm RA, because it can occur in other conditions and in a portion of healthy individuals, particularly older adults. The presence of RF is considered alongside clinical findings and other tests, such as anti-cyclic citrullinated peptide (anti-CCP) antibodies, which are more specific for RA.

RF can be positive in a range of other diseases, including Sjögren's syndrome, systemic lupus erythematosus, vasculitis, chronic infections (notably hepatitis C and HIV), and certain malignancies. False positives and false negatives can occur, so RF results should be interpreted within the broader clinical picture.

In practice, RF is part of RA classification and differential diagnosis, used with clinical evaluation and other serologic markers rather than as a definitive diagnostic test.