Rheumatoid Factor (RF)
Rheumatoid factor is an antibody (usually IgM) that targets the Fc portion of IgG. It was the first blood marker described for rheumatoid arthritis (RA) and is positive in 70–80% of RA patients. However, RF is also found in Sjögren's syndrome, hepatitis C, chronic infections, other autoimmune diseases, and 5–10% of healthy adults — particularly the elderly — so it is sensitive but not specific. Anti-CCP has largely replaced RF as the most useful RA-specific antibody.
Expected Result
Normal
Negative (<14 IU/mL)
Method-dependent cutoff; many labs use <14 or <20 IU/mL. Often reported as titre in older methods.
This is a qualitative test — results are reported as positive or negative rather than as a numeric range. Interpretation may vary by laboratory method; always review with your doctor.
What a Negative Result Means
A negative RF makes classical RA less likely but does not exclude it — about 20–30% of RA patients are seronegative. Anti-CCP should also be checked since it has higher specificity and is sometimes positive when RF is negative. Seronegative arthritis has its own differential (spondyloarthropathy, psoriatic arthritis).
What a Positive Result Means
A positive RF supports RA in the right clinical setting (symmetric small-joint inflammation, morning stiffness). Higher titres correlate with more aggressive disease and extra-articular features (nodules, vasculitis, lung involvement). RF can also be positive in Sjögren's (up to 70%), hepatitis C, chronic viral or bacterial infection, cryoglobulinemia, and 5–10% of the elderly without disease.
Frequently Asked Questions
What is the difference between RF and anti-CCP?
RF is sensitive but not specific — many non-RA conditions raise it. Anti-CCP (cyclic citrullinated peptide) is highly specific for RA (95%+) and appears years before symptoms. Testing both is standard — a patient with both positive has a very high probability of RA and often more aggressive disease.
My RF is positive but I have no joint symptoms. What now?
A positive RF without clinical features is usually not RA. Check anti-CCP — if also positive and titres are high, close follow-up for emerging RA is wise. If anti-CCP is negative, RF alone is rarely meaningful. Hepatitis C, Sjögren's syndrome, and age-related false positivity are common alternative explanations.
Can RF become negative after treatment?
Sometimes. In aggressive RA on biologic therapy, RF titres can drop as disease activity controls. This does not reverse the diagnosis but is a good prognostic sign. Anti-CCP is more stable and less likely to normalize with treatment.
Related Autoimmune tests
See all →Anti-TPO Antibody
Antibody against thyroid peroxidase — key marker of autoimmune thyroiditis.
IU/mLAutoimmuneANA (Antinuclear Antibody)
Screening test for autoimmune connective tissue disease, especially lupus.
AutoimmuneAnti-dsDNA Antibody
Highly specific antibody for systemic lupus erythematosus (SLE).
AutoimmuneAnti-CCP Antibody
Highly specific rheumatoid arthritis antibody — often positive before symptoms.
This information is for educational purposes only and should not replace professional medical advice. Always consult your doctor for interpretation of your test results.
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