From the Guidelines
The Rheumatoid Factor (RF) test is primarily used to help diagnose rheumatoid arthritis (RA) and monitor disease activity, with its main uses including diagnosis, disease monitoring, prognosis, screening, and differential diagnosis. Here are the main uses:
- Diagnosis: RF is a key blood test in diagnosing RA, especially when combined with other clinical symptoms and tests, as seen in the 2010 ACR/EULAR Classification Criteria for Rheumatoid Arthritis 1.
- Disease monitoring: RF levels can be used to track the progression of RA and assess treatment effectiveness.
- Prognosis: Higher RF levels often correlate with more severe disease and poorer outcomes in RA patients, as noted in the assessment of disease severity and prognosis 1.
- Screening: RF may be used to screen for RA in patients with unexplained joint pain or inflammation.
- Differential diagnosis: RF testing can help distinguish RA from other types of arthritis or autoimmune conditions, such as systemic lupus erythematosus, psoriatic arthritis, and gout 1. While RF is not specific to RA and can be present in other conditions, it remains a valuable tool in rheumatology, with a positive RF test (typically >20 IU/mL) combined with clinical symptoms strongly suggesting RA, but diagnosis should always be made by a rheumatologist considering all available information 1. It's also important to note that about 20% of RA patients are RF-negative, so a negative test doesn't rule out the disease. The 2010 ACR/EULAR Classification Criteria for Rheumatoid Arthritis provides a score-based algorithm for classifying RA, which includes serologic findings such as RF and anti-citrullinated protein antibody (ACPA) 1.
From the Research
Uses of Rheumatoid Factor (RF)
- Rheumatoid factor (RF) is used as a biomarker for the diagnosis of rheumatoid arthritis (RA) 2, 3, 4, 5, 6
- RF is used to diagnose RA early and prevent joint destruction before irreversible damage occurs 2
- RF is used in combination with other biomarkers, such as anti-cyclic citrullinated peptide antibody (anti-CCP) and matrix metalloproteinase-3 (MMP-3), to improve diagnostic accuracy 2, 3
- RF is used to evaluate the prognosis of RA and to monitor disease activity 5
- RF levels are used to predict treatment responsiveness to tumor necrosis factor (TNF) inhibitors and other drugs 5
- RF is used as a marker for other rheumatic diseases, such as primary Sjögren's syndrome 4
- RF levels are used to assess the risk of organ damage and life prognosis in patients with RA 5
Limitations of RF
- RF has low specificity for RA, meaning that it can be positive in patients with other rheumatic diseases or in healthy individuals 2, 6
- RF has limited sensitivity for RA, meaning that it can be negative in some patients with RA 2, 4
- RF levels can be influenced by other factors, such as age, infections, and autoimmune diseases 6
Combination with Other Biomarkers
- Combining RF with other biomarkers, such as anti-CCP and MMP-3, can improve diagnostic accuracy and specificity for RA 2, 3
- Combining RF with IgA RF and anti-citrullinated protein antibodies (ACPA) can increase specificity for RA classification 4
- Combining RF with other biomarkers can help to identify patients with high disease activity and progressive joint destruction 5