What is rheumatoid factor?
This test measures levels of rheumatoid factor antibodies. Rheumatoid factor (RF) is an autoantibody that is produced by the body’s immune system. These antibodies attack the body’s own tissue. The presence of this antibody is indicative of inflammatory and autoimmune activity. It is used in the diagnosis of rheumatoid arthritis, often alongside ACPA antibodies (CCP).
Why test rheumatoid factor?
Symptoms
Including pain, warmth, swelling, and joint stiffness. An RF test may be repeated when the first test is negative, and symptoms persist.
Family history
You have a family history of rheumatoid arthritis and/or concerns about developing it.
Health history
You have an autoimmune condition or a clinical picture that suggests a test may be useful.
What do the results mean?
What does a negative test mean?
A negative RF test means that you do not have antibodies to rheumatoid factor, but it cannot rule out rheumatoid arthritis. Rheumatoid arthritis is a clinical diagnosis made by considering symptoms in conjunction with tests.
Around 20% of those with RA will have no detectable RF or very low levels. A CCP antibody test can help to complete the picture and determine whether someone has RA or not. We recommend that those who have symptoms take both tests together.
What does a positive test mean?
A positive RF test means that you have antibodies to rheumatoid factor. The rheumatoid factor test is looked at together with other lab tests and a person's signs, symptoms, and clinical history. RF is not diagnostic of RA. However, it is present in 70%-90% of patients who have RA.
In those who have clinical signs and symptoms of rheumatoid arthritis, significant concentrations of rheumatoid factor indicate a high likelihood of RA.
More information
The rheumatoid factor (RF) test is primarily used to help diagnose rheumatoid arthritis (RA) and to help distinguish RA from other forms of arthritis or other conditions that cause similar symptoms.
Diagnosis of RA relies heavily on the clinical picture, i.e. the signs and symptoms of the disease. However, some may not be present or follow a typical pattern, especially early in the disease. They may not always be clearly identifiable, since people with RA may also have other disorders, as it is common to have autoantibodies against several tissues. The RF test is one tool among others that can be used to help make a diagnosis when RA is suspected.
Rheumatoid factor is the most common test for rheumatoid arthritis, although it has been supplemented (and sometimes replaced) by the newer ACP antibody test (ACPA). A 2012 study concluded that ‘individuals in the general population with elevated rheumatoid factor have up to 26-fold greater long- term risk of rheumatoid arthritis, and up to 32% 10-year absolute risk of rheumatoid arthritis. These novel findings may lead to the revision of guidelines for early referral to a rheumatologist and early arthritis clinics based on rheumatoid factor testing.
Rheumatoid factor can occur in several forms, but the form IgM has proven to have the highest sensitivity in people of European origin * and is found in 60-80% of people with rheumatoid arthritis in the group.
Instructions
No advance preparation is needed for this test.
On the day of the test
Remember to take I.D. with you when going to take a test.
Arrive early and sit down quietly for 15 minutes before the test is taken.