Rheumatoid factor (RF)
What is Rheumatoid Factor (RF)
Rheumatoid factor (RF) is a protein antibody produced by the body’s immune system. It is normally found in low levels in healthy individuals, while a high level may indicate an autoimmune disorder such as rheumatoid arthritis. Other conditions such as lupus, mixed connective tissue disease, and scleroderma may also be indicated by high levels of RF.
Preparation
In the preparation for a RF test, no special preparation is necessary. Patients should inform their doctors of any current medications prior to the test.
Procedure
To measure the rheumatoid factor, a small sample of blood is taken from a vein in the arm via a needle and sent to a lab for analysis. The results usually take a few days.
Types
- IgM-RF
- IgA-RF
- Complement-fixing rheumatoid factor (CF-RF)
- Combined IgM-IgA-CF-RF
Risks
As with most blood tests, there is a small risk of infection and bleeding at the site of the injection as well as general complications associated with any form of needle injection. There are also risks related to the results of the test. A false positive (in which a healthy person is incorrectly identified as having an autoimmune disorder) or a false negative (in which an autoimmune disorder is not correctly identified) may lead to inappropriate medical care.
When is it used?
RF is usually measured as part of a comprehensive workup when an autoimmune disorder such as rheumatoid arthritis is suspected. It is used to help confirm a diagnosis, differentiate between different types of arthritis, and guide treatment decisions.
Limitations
A single high measurement of RF does not necessarily indicate the presence of an autoimmune disorder; however, a persistently elevated level of RF can indicate the presence of disease. Furthermore, some patients with an autoimmune disorder may have normal levels of RF or their levels may be low. For this reason, other tests such as a complete blood count (CBC) and C-reactive protein (CRP) may also be ordered to help confirm a diagnosis.
