What it measures
Rheumatoid factor (RF) is an antibody that targets the body's own IgG antibodies. It is measured in serum. Most people with rheumatoid arthritis have it, but so do some healthy people.
Why people test it
- Measured when rheumatoid arthritis is suspected, for example with painful, swollen joints.
- Often tested alongside anti-CCP antibodies.
- Investigating Sjögren's syndrome, lupus and some other autoimmune conditions.
Typical range
Gloucestershire Hospitals' laboratory gives a range of 0 to 14 IU/mL. Ranges vary by lab, method, age and sex, and your report shows the lab's own range. Source: Gloucestershire Hospitals NHS Foundation Trust, Pathology: Rheumatoid factor.
Finger-prick or vein?
Providers offer this test only from a vein sample, taken at a clinic or by a visiting nurse.
A positive result does not diagnose rheumatoid arthritis on its own. RF is found in some healthy people, and not everyone with the condition has it.