Interpret Your Rheumatoid Factor Results
Enter your RF value below and get an instant, free AI interpretation — a plain-English explanation checked against WHO/IFCC reference ranges.
Medical Disclaimer
This AI-generated interpretation is for educational purposes only and does not constitute medical advice, diagnosis, or treatment. Results may vary based on individual health factors not captured here.
Always consult a qualified healthcare professional before making any health decisions. Read full disclaimer →
Rheumatoid Factor Normal Ranges
Rheumatoid Factor (RF) is an autoantibody — typically IgM — directed against the Fc portion of IgG immunoglobulin.
| Reference Range | Unit | Notes |
|---|---|---|
| 0 – 14 | IU/mL | Negative <14 |
Why Doctors Order the Rheumatoid Factor Test
RF is positive in approximately 70–80% of rheumatoid arthritis patients, but also in 5–10% of healthy adults (especially the elderly), and in many non-RA conditions (Sjögren's syndrome, SLE, hepatitis C, bacterial endocarditis, sarcoidosis, tuberculosis).
How to Enter Your RF Result
Enter your RF value in IU/mL, exactly as shown on your lab report.
What a Low or High RF Can Be Associated With
Below the reference range
- Approximately 20–30% of RA patients are "seronegative" — RF negative — especially early in disease
- Negative RF does not exclude RA (seronegative RA exists)
Above the reference range
- Rheumatoid Arthritis (RA) — most common clinical indication
- Sjögren's syndrome (often very high RF)
- SLE (systemic lupus erythematosus)
- Hepatitis C (associated with cryoglobulinemia and high RF)
- Bacterial endocarditis and other chronic infections
These are common associations, not a diagnosis. A single result is read alongside your symptoms, history and other tests — discuss it with your doctor.
What Can Change Your RF Result
Before you read too much into a result, consider whether any of these applied:
- Age (RF positivity increases with age — up to 25% of people over 70 are RF positive without RA)
- Chronic infections (hepatitis C most notably causes very high RF)
- Some assays detect IgM-RF only; others detect IgG- and IgA-RF as well
- Hypergammaglobulinemia can cause false-positive RF
Preparing for the test: No fasting required. RF can be measured from a random blood sample.
Symptoms That Often Prompt RF Testing
- Morning joint stiffness lasting more than 60 minutes
- Symmetric joint swelling (typically small joints: MCP, PIP, wrists)
- Joint pain and tenderness
- Rheumatoid nodules (subcutaneous lumps at pressure points)
- Fatigue and malaise
Want the full clinical guide to Rheumatoid Factor?
Reference ranges, causes, symptoms, preparation, and FAQs.