Rheumatoid factor (RF)
Autoantibody in the blood measured when rheumatoid arthritis is being investigated
Also known as
Definition
Rheumatoid factor is an antibody made by the immune system that does not target germs but the body's own antibodies, usually immunoglobulin G. The immune system makes it by mistake or when it is overactive while fighting an infection. Many healthy people have small amounts in their blood. The test is mainly used together with other tests to investigate rheumatoid arthritis. On its own it does not make a diagnosis.
| Parameter | Value |
|---|---|
| Unit | IU/ml or titer |
| Reference Range | MedlinePlus lists a normal value below 15 IU/ml or, when reported as a titer, below 1:80. Many labs report only positive or negative. Cut-offs differ between test methods; the range printed on your report is what counts. Discuss the result with your doctor. |
Agree on your personal target range with your doctor.
1 IU/ml equals 1 kIU/l (same number).
↓ What a low value means
A negative result means little or no rheumatoid factor was found in the blood. This is the normal finding. It does not rule out rheumatoid arthritis or another condition, though, because people with rheumatoid arthritis can also have little or no rheumatoid factor. If you have matching symptoms, your doctor may order further tests.
↑ What a high value means
A positive result can be related to rheumatoid arthritis or Sjögren syndrome, as well as other autoimmune diseases such as lupus or scleroderma, chronic infections such as hepatitis C, tuberculosis or endocarditis, chronic lung or liver disease, and certain cancers. The higher the value, the more likely such a link is. Healthy people can also have raised values. Discuss any deviation with your doctor.
When to test
The test is usually ordered with signs of rheumatoid arthritis, such as joint pain and stiffness that are worse in the morning or after rest, swollen, warm or tender joints on both sides, fatigue, fever, or bumps under the skin near the joints. It is rarely measured without symptoms. No special preparation is needed.
Frequently asked questions
What is the difference between rheumatoid factor and anti-CCP antibodies? +
Both are measured when rheumatoid arthritis is suspected. According to MedlinePlus, anti-CCP antibodies are more specific for rheumatoid arthritis than rheumatoid factor, which can also be raised in many other conditions and in healthy people. That is why both values are often looked at together.
Can rheumatoid factor be raised in healthy people? +
Yes. Many healthy people have small amounts of rheumatoid factor in their blood, and even higher values are not always a sign of disease. The assessment depends on symptoms, medical history and other findings.
Does the test help with osteoarthritis? +
No. Osteoarthritis is not an autoimmune disease and does not involve rheumatoid factor. The test is not used to investigate osteoarthritis.
What does a negative rheumatoid factor mean if my joints hurt? +
A negative result does not rule out rheumatoid arthritis. If typical symptoms are present, your doctor may order further tests or refer you to a rheumatologist.
Rheumatoid factor (RF)
Sources
Last updated: October 05, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.