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 of RA. 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 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 test 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 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 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.