Rheumatoid Factor (RF)
Rheumatoid factor (RF) is an autoantibody that targets the body’s own tissues, particularly immunoglobulin G (IgG). Testing for RF is used primarily in the evaluation and diagnosis of rheumatoid arthritis (RA), a chronic autoimmune disease that primarily affects the joints. Here’s how RF testing is used:
- Diagnosis of Rheumatoid Arthritis (RA): RF testing is one of the laboratory tests commonly used in the diagnosis of RA. Elevated levels of RF are found in a significant proportion of individuals with RA, particularly those with more aggressive or seropositive disease. However, it's important to note that RF can also be present in individuals without RA and in other autoimmune diseases and infections. Therefore, RF testing is not sufficient for a definitive diagnosis of RA but is considered along with clinical symptoms, physical examination findings, and other laboratory tests.
- Assessment of Disease Activity: In individuals with established RA, RF levels may correlate with disease activity. Higher levels of RF are often associated with more severe joint inflammation, progressive joint damage, and systemic manifestations of RA. RF testing may be used as one of the markers to assess disease activity and monitor response to treatment over time.
- Prognostic Marker: Elevated RF levels at the time of diagnosis or during follow-up may be associated with a worse prognosis in individuals with RA. Higher RF levels have been linked to increased risk of joint destruction, functional impairment, and development of extra-articular manifestations of RA, such as rheumatoid nodules and vasculitis.
- Screening for Autoimmune Diseases: RF testing may also be used as part of the evaluation for other autoimmune diseases, such as Sjögren's syndrome, systemic lupus erythematosus (SLE), and mixed connective tissue disease (MCTD). Elevated RF levels can be found in some individuals with these conditions, although it is less specific compared to RA.
- Assessment of Response to Treatment: RF levels may be monitored over time to assess response to treatment in individuals with RA. Reductions in RF levels following treatment with disease-modifying antirheumatic drugs (DMARDs), biologic therapies, or other interventions may indicate improvement in disease activity and prognosis.