What is
Rheumatoid Factor?

Rheumatoid factor (RF) is commonly evaluated when diagnosing rheumatoid arthritis. Why is this blood test used? Should you be worried if it comes back positive?

What is Rheumatoid Factor?

RF is an anti-body in the blood, specifically an immunoglobulin M protein that is produced by the body’s immune system. Anti-bodies function in the body by attaching to specific antigens (foreign particles in the body), and removing them from the body. This is how your immune system attacks and removes bacteria and viruses.

The issue with autoantibodies is that they perceive the patient’s own tissues as foreign, thus attacking healthy tissues. It is believed that rheumatoid factor elevates the body’s immune response, which in turn leads to tissue destruction.

What does this test mean?

blood tests

When symptoms are consistent with rheumatoid arthritis and there is an elevated RF, there is a strong likelihood that you have rheumatoid arthritis. An elevated RF is generally considered 20 IU/ml. However, if the RF test does not come back as being elevated, this does not mean the diagnosis of rheumatoid arthritis is ruled out. A negative or normal RF test occurs in 20% of those that are diagnosed with rheumatoid arthritis.

It is also important to note that the RF test is not a diagnostic test. Rather, it is used in conjunction with potential rheumatoid arthritis symptoms and other tests to reach a diagnosis. In addition, false positive results can occur. This means the test comes back positive for elevated RF when in fact it is not. The incidence of false positive test increases with age.

Elevated RF is also not an indication of the severity of inflammatory symptoms. Some with elevated RF have no symptoms at all. Elevated RF is not only associated with rheumatoid arthritis but can also be associated with other conditions including systemic lupus, cancer, viral infections, and other diseases of the liver, kidneys, and lungs.

How is RF tested?

RF is tested via a blood test and may be ordered with other rheumatoid arthritis blood tests for making the diagnosis of RA.

It is important to know that rheumatoid arthritis factor is only one aspect of obtaining a diagnosis of rheumatoid arthritis. Communicate with your doctor regarding the nature of such tests and what that means in relation to your overall diagnosis.

Return to Top

Return from Rheumatoid Factor to Rheumatoid Arthritis Symptoms