What is being tested?
This test detects evidence of rheumatoid factor (RF), which is a type of autoantibody. An antibody is a protective protein that forms in the blood in response to a foreign material, known as an antigen (for example a bacterial protein). Autoantibodies, however, are antibodies that attack one's own proteins rather than foreign protein. Rheumatoid factors are autoantibodies directed against the class of immunoglobulins known as IgG and are members of a class of proteins that become elevated in states of inflammation.
Rheumatoid factor is elevated in many patients with both chronic and acute inflammation; it may be used to monitor the level of inflammation associated with rheumatoid arthritis (RA). Other markers such as CRP are considered more accurate for disease monitoring. Experts still do not understand exactly how RF is formed or why, but it is believed that RF probably does not directly cause joint damage but that it helps to promote the body's inflammation reaction, which contributes to the tissue destruction seen in rheumatoid arthritis.
How is it used?
The test for rheumatoid factor (RF) is used to help diagnose rheumatoid arthritis (RA). The test may also be used to help diagnose an arthritis-related condition called Sjögren’s syndrome. About 80 to 90 per cent of patients with this syndrome have high amounts of RF in their blood although it can take years to appear.
When is it requested?
The test for RF is ordered when you have signs of RA. Symptoms may include stiffness in your joints for a long time in the morning, swelling, nodules under your skin, and evidence on X-rays of swollen joint capsules and loss of cartilage and bone if the disease has progressed.
If you still have symptoms of RA but your first RF test is negative, the test may need to be repeated. The levels may vary over time.
Another test that may be useful is antibody testing for anticyclic citrullinated peptide (CCP antibodies) as these may be detected when RF is negative.
The RF test also may be ordered to help diagnose Sjögren’s syndrome. Symptoms include extremely dry mouth and eyes, dry skin, and joint and muscle pain. Many connective tissue disorders are autoimmune diseases, and RA and other diseases, such as Raynaud’s syndrome, scleroderma, autoimmune thyroid disorders and systemic lupus erythematosis are common among people with Sjögren's syndrome.
What does the result mean?
The presence of RF indicates that you may have rheumatoid arthritis. Positive RF test results are found in the majority of cases of rheumatoid arthritis. In addition, more than 50% of patients with high levels of RF in their blood have Sjögren’s syndrome. Some patients with RA also have Sjögren’s syndrome. (Women more often have both of these diseases. About two to three times as many women as men have RA, and women have 90 per cent of the cases of Sjögren’s syndrome.)
If you have a positive RF test result but do not have RA or Sjögren’s syndrome, there may be another reason, such as endocarditis, systemic lupus erythematosus (lupus), tuberculosis, syphilis, sarcoidosis, cancer, viral infection, or disease of the liver, lung, or kidney. You may also test positive if you have received skin or kidney grafts from a person who does not have your identical genetic profile.
A negative RF test result may mean that you do not have RA, or it is too early in your disease progression to detect RF. If your symptoms appear to be those of RA or Sjögren’s syndrome, your doctor may order the RF test again as your condition progresses.
Is there anything else I should know?
The RF test has a high false positive rate and the result must be used along with the patient’s symptoms and history to make a diagnosis of rheumatoid arthritis, Sjögren’s syndrome, or another condition.
Interfering factors for the RF test generally include having many vaccinations or lipaemia (a large amount of fats in the blood). Methyldopa, a blood pressure drug, can increase the amount of RF detected by the test.
Common questions
Not necessarily. While it is true that high amounts of RA are found in people with a severe, active case of rheumatoid arthritis, high levels may also result from Sjögren’s syndrome or other inflammatory conditions. Increased RF levels in your blood also can mean that you have endocarditis, systemic lupus erythematosus (lupus), tuberculosis, syphilis, sarcoidosis, cancer, viral infection, or disease of the liver, lung or kidney, among other diseases. You may also test positive if you have received skin or kidney grafts from a person who does not have your identical genetic profile.
Not necessarily. In a few people, RA lasts only a few months or perhaps a year or two and then goes away without causing any real damage though those individuals tend to be RF negative. Other people have mild or moderate disease, with periods of worsening symptoms, called flares. Still others have a severe form of the disease that is active most of the time and leads to serious joint damage. The presence of anti-CCP antibodies marks a group of those with RA that will have persistent long term disease.
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