Rheumatoid Factor
An autoantibody associated with rheumatoid arthritis and some other conditions.
| Typical reference range | below 14 IU/mL |
Ranges vary by laboratory, method, age and sex: always use the range printed on your own report. Why labs differ.
What it measures
Rheumatoid factor is an antibody, usually IgM, directed against the body's own IgG antibodies.
Why it matters
RF supports a diagnosis of rheumatoid arthritis, where about 70-80% of patients test positive, and higher levels are associated with more severe disease. It is less specific than anti-CCP antibodies.
What a high result can mean
Positive results occur with rheumatoid arthritis, Sjogren's syndrome, lupus, chronic infections (hepatitis C, endocarditis), cryoglobulinemia and some lymphomas, and in 5-10% of healthy people, rising with age.
What a low result can mean
A negative result is normal but does not rule out rheumatoid arthritis.
What affects the result
Interpret with symptoms, anti-CCP antibodies, CRP and ESR.
Units and conversion
Usually reported in IU/mL.
- From kIU/L: multiply by 1 to get IU/mL
- From U/mL: multiply by 1 to get IU/mL
Also called on lab reports
RF, RA Factor, Rheumatoid Factor, Quant, Rheumatoid Factor (RF), RA Latex Turbid.
Related tests: Inflammation & Immunity
This page is educational and does not replace advice from a healthcare professional.