From the Guidelines
Rheumatoid factor (RF) is an antibody that is often present in the blood of individuals with rheumatoid arthritis (RA), a chronic autoimmune disorder that primarily affects the joints.
Key Characteristics of RF
- It is an immunoglobulin M (IgM) antibody that is directed against the Fc portion of immunoglobulin G (IgG)
- Can be used as a diagnostic marker to help identify RA, although it is not exclusive to this condition and can be found in other autoimmune diseases, infections, and healthy individuals 1
Detection and Interpretation of RF
- The presence of RF can be detected through a blood test, with elevated levels typically indicating a higher likelihood of RA or another autoimmune disorder
- The level of RF can be used to support a diagnosis of RA, but it is not diagnostic on its own and should be considered in conjunction with other clinical and laboratory findings 1
Clinical Significance of RF
- RF is one of the serologic markers used in the classification criteria for RA, along with anti-citrullinated protein antibody (ACPA)
- The presence of RF can also be associated with a higher risk of developing RA in individuals with undifferentiated arthritis or other autoimmune disorders 1
Limitations and Considerations
- RF is not specific to RA and can be found in other conditions, such as systemic lupus erythematosus, psoriatic arthritis, and gout
- The absence of RF does not exclude a diagnosis of RA, as some patients with RA may be seronegative 1
From the Research
Definition of Rheumatoid Factor (RF)
- Rheumatoid factor (RF) is a family of autoantibodies against the Fc part of IgG 2
- RF is a polyclonal autoantibody directed against the Fc portion of IgG 3
- RF recognizes epitopes in the Fc region of immunoglobulin (Ig) G and correlates with the clinical severity of rheumatoid arthritis (RA) 4
Characteristics of RF
- RF can be of different isotypes, including IgM, IgA, and IgG 2, 5
- IgG-RF attracts pathogenic interest, but its detection remains technically challenging 2
- The specificity of serum RF and RF produced by rheumatoid synovial cells (RSC) is different 3
- RF can bind to different subclasses of IgG, including IgG1, IgG2, IgG3, and IgG4 2, 3, 4
Clinical Significance of RF
- Detection of RF in the serum of patients with rheumatoid arthritis (RA) was one of the first indications of autoimmunity in RA 6
- RF is a well-established marker for the diagnosis and classification of rheumatoid arthritis (RA) 5
- Patients with RF-positive RA generally have more severe disease than those with RF-negative RA 6
- Combined positivity for IgA RF, IgM RF, and IgG ACPA has a higher specificity and lower sensitivity for RA classification than positivity for either of the antibodies 5