Rheumafaktor

Rheumafaktor, also known as rheumatoid factor (RF), is an autoantibody commonly of the IgM isotype that binds to the Fc portion of human IgG. RF can be detected in blood using immunoassays such as nephelometry or ELISA. Results are reported as a titer or as a qualitative positive/negative result, with the exact cut-off dependent on the assay.

Clinically, RF is most associated with rheumatoid arthritis (RA). It is present in about 60-80% of people with established RA, and its prevalence increases with disease duration. However, RF is not specific to RA; it can be detected in other autoimmune diseases (for example Sjögren’s syndrome, systemic lupus erythematosus), chronic infections, liver disease, and in a subset of healthy older adults. Therefore a positive RF test does not confirm RA by itself.

RF is often interpreted together with anti-cyclic citrullinated peptide antibodies (ACPA). ACPA has higher specificity for RA, and the combination improves diagnostic accuracy. In some patients, RF titres correlate with disease activity or prognosis, with higher levels associated with more severe disease and extra-articular manifestations, though this is not universal.

RF testing is not recommended as a general screening tool for the healthy population and is not used alone to monitor disease activity. Seronegative RA patients may have a negative RF test despite active disease.