Rheumatoid Factor
Overview
Rheumatoid factor (RF) measures autoantibodies, primarily IgM, directed against the Fc portion of IgG immunoglobulins in serum. It reflects immune complex formation and B-cell activation relevant to autoimmune processes. Elevated levels may indicate rheumatoid arthritis, Sjögren’s syndrome, or other autoimmune conditions, while low levels are typical in healthy individuals; it is clinically useful for supporting rheumatoid arthritis diagnosis, assessing disease severity, and monitoring treatment response, though specificity is limited as it can appear in infections and other disorders.Clinical Use Cases
- Supporting diagnosis of rheumatoid arthritis (with other criteria).
- Assessing prognosis in RA (higher titers correlate with erosive disease).
- Evaluating Sjögren’s syndrome and mixed connective tissue disease.
- Monitoring disease activity and treatment response.
- Investigating chronic infections or malignancies with positive RF.
Specimen Types
- Serum.
- Plasma (less common).
Measurement Methods
- Nephelometry (quantitative, common).
- Turbidimetry.
- Latex agglutination (semiquantitative screening).
- Enzyme-linked immunosorbent assay (ELISA).
Test Preparation and Influencing Factors
- No fasting required.
- No specific timing restrictions.
- Elevated nonspecifically in infections, liver disease, cancer, or aging.
- Immunosuppressive therapy may lower levels.
- Sample hemolysis or lipemia can interfere with assays.
Synonyms
- RF.
- IgM rheumatoid factor.