Rheumatoid Factor (RA Factor)
- Sample Type
- Serum
- Fasting
- No
- Unit
- IU/mL
Function
Rheumatoid Factor (RF) is an autoantibody, specifically an immunoglobulin (usually IgM) that targets the Fc portion of the patient's own IgG antibodies. The presence of these autoantibodies leads to the formation of immune complexes that deposit in tissues, primarily the synovium of joints, triggering a cascade of inflammatory responses and tissue damage.
Why it is Ordered
The RF test is primarily ordered when a clinician suspects Rheumatoid Arthritis (RA) or Sjögren's Syndrome. It is used as part of a diagnostic panel alongside Anti-CCP antibodies and inflammatory markers like ESR and CRP. It is particularly useful for differentiating inflammatory arthritis from non-inflammatory conditions like osteoarthritis.
Associated Conditions
- Rheumatoid Arthritis: Approximately 70-80% of patients with RA will test positive for RF, though a negative result does not rule out the disease (seronegative RA).
- Sjögren's Syndrome: A high percentage of patients with this autoimmune disorder also present with elevated RF.
- Chronic Infections: RF can be elevated in conditions such as Hepatitis C, Endocarditis, and Tuberculosis.
- Other Autoimmune Diseases: Systemic Lupus Erythematosus (SLE) and Mixed Connective Tissue Disease (MCTD) can show positive RF levels.
- Healthy Aging: A small percentage of healthy elderly individuals may naturally have low levels of RF without clinical disease.
Check Your Result
Check Your Result
Enter your lab result to see where you stand compared to the standard reference range.
Why Context Matters
A second opinion or follow-up testing is often necessary because the RF test has a high rate of 'false positives' in the context of RA. RF is not specific to Rheumatoid Arthritis; it can be elevated due to chronic viral or bacterial infections, recent vaccinations, or even other autoimmune disorders. Furthermore, laboratory methods vary, and a borderline result in one lab might be interpreted differently in another. Because a diagnosis of RA often leads to life-long immunosuppressive therapy, confirming the result with a more specific test like Anti-CCP is standard practice.
Lab ranges are statistical averages, not biological laws. "Normal" for a 20-year-old male isn't normal for a 60-year-old female.
Clinical References
Source-of-truth databases and clinical guidelines for Rheumatoid Factor (RA Factor):
Official Sources
- Clinical Practice Guidelines | American College of Rheumatologyrheumatology.org
Research & Guidelines
Related Indicators
Medically Reviewed by Dr. Binoy Babu, MBBS
Board Certified Doctor • 10+ Years Clinical Experience
Dr. Babu is a practicing physician dedicated to empowering patients with clear, actionable medical information. He founded 2opi to bridge the gap between complex lab reports and patient understanding, ensuring everyone has access to a reliable second opinion.
Get Notified When Dr. Babu Is Available