Rheumatoid factor (RF)
Also called: Rheumatoid factor, RF
An antibody found in most people with rheumatoid arthritis — but also in many healthy older adults and in other conditions. It is a sensitive but not specific screen, best read together with anti-CCP, which is far more specific for RA.
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What does Rheumatoid factor (RF) measure?
Rheumatoid factor is an antibody directed against part of the body's own immunoglobulin. It is positive in roughly 70–80% of people with rheumatoid arthritis, which makes it a useful screen when inflammatory joint disease is suspected. But it is not specific: it also appears in Sjögren's syndrome, other autoimmune diseases, chronic infections (notably hepatitis C), and in a meaningful minority of perfectly healthy people, more so with age. So a positive RF supports but does not prove RA, and a negative RF does not exclude it (about 20–30% of RA is 'seronegative'). This is why modern practice pairs RF with anti-CCP antibodies and inflammatory markers.
What does a high Rheumatoid factor (RF) level mean?
- Rheumatoid arthritis — positive in ~70–80%; higher titres associate with more aggressive, erosive disease.
- Sjögren's syndrome — often strongly positive.
- Other autoimmune disease — SLE, systemic sclerosis, mixed connective-tissue disease.
- Chronic infection — hepatitis C (often with cryoglobulins), endocarditis, tuberculosis.
- Healthy people — a low-titre positive is common, especially over 65.
- Chronic lung or liver disease.
What does a low Rheumatoid factor (RF) level mean?
- Negative / normal — reduces but does not exclude RA; seronegative RA exists.
- Anti-CCP may still be positive — a negative RF with a positive anti-CCP still strongly supports RA.
When to discuss with a doctor
RF is worth checking when there is genuine suspicion of inflammatory arthritis — persistent symmetrical joint pain and swelling, prolonged morning stiffness — ideally alongside anti-CCP, ESR and CRP. A positive RF alone in someone without joint symptoms is usually not RA and should not cause alarm. A positive RF or anti-CCP with inflammatory joint symptoms should go to rheumatology promptly, because early treatment prevents joint damage. Because RF tracks with hepatitis C and Sjögren's, the context matters. Mediora.AI shows RF together with anti-CCP and the inflammatory markers so the pattern — not a lone positive — is what's read; the diagnosis belongs with rheumatology.