When your doctor thinks that you have symptoms suggestive of RA or Sjögren’s syndrome
A blood sample taken from a vein in your arm
This test detects and measures the presence of autoantibodies like rheumatoid factor (RF), and anti-cyclic citrinullated protein antibodies (ACPA), which are associated with rheumatoid arthritis in the blood. We all have antibodies (also known as immunoglobulins) in our blood, which are protective proteins which defend the body against “foreign” agents of infection, particularly from bacteria. However, autoantibodies are antibodies that attack the patient’s tissues, such as bones and cartilage. While the role of RF and ACPA are not well understood, they may not directly cause joint damage, but promote the body's inflammation reaction, contributing to autoimmune joint destruction.
The RF and ACPA tests are sensitive but ACPA has higher specificity because RF can be found in diseases other than rheumatoid arthritis (RA). RF can be present in other autoimmune disorders, such as Sjögren syndrome, in some persistent bacterial and viral infections, and can be found in a small but significant percentage of healthy people particularly in the elderly.
Some genome-wide association studies (GWAS) have identified the detection of genetic factors like class II human leukocyte antigen (HLA) genes as the most specific testing, useful even before clinical symptoms of rheumatoid arthritis.
How is it used?
The rheumatoid factor (RF) test is used to help diagnose RA and to distinguish it from other forms of arthritis and other conditions that cause similar symptoms of joint pain, inflammation, and stiffness, but it is only one of several clinical and laboratory factors. It may be requested with other autoimmune related tests, such as ANA (antinuclear antibody), markers of inflammation, such as CRP (C-reactive protein) and ESR (erythrocyte sedimentation rate), and with FBC (Full Blood Count) to evaluate the body’s blood cells.
Cyclic Citrullinated Peptide Antibody (CCP) is a test that can help detect early RA. Patients with rheumatoid arthritis can have positive tests for either RF or CCP or may have both antibodies detected.
If the rheumatoid factor is positive and the clinical suspicion is of Sjogren’s syndrome, additional tests may be taken e.g. anti Ro (SSA) and anti La (SSB) if the ANA is positive.
When is it requested?
The test for RF may be requested when a patient has signs of RA and these have persisted for more than 6 weeks. Symptoms may include pain, warmth, swelling, and morning stiffness in the joints, nodules under the skin, and, if the disease has progressed, evidence on X-rays of swollen joint capsules and loss of cartilage and bone. An RF test may be repeated when the first test is negative and symptoms persist. The RF test also may be requested when a patient has symptoms suggesting Sjögren’s syndrome. Symptoms may include an extremely dry mouth and eyes, and joint and muscle pain. Symptoms may also be mixed as patients may have more than one autoimmune disorder. Sjogren’s syndrome can occur by itself or following RA, or systemic lupus eryhtematosus (SLE). Patients with RA and/or Sjogren’s syndrome may also have other autoimmune disease such as thyroid disorders.
What does the test result mean?
In patients with symptoms and clinical signs of RA the presence of significant concentrations of RF indicates that it is likely that they have rheumatoid arthritis (RA). 70-90% of patients with RA have positive RF test. In patients with symptoms of Sjögren’s syndrome, of the presence of RF can indicate that they have the condition. RF is found in 75-95% of patients with Sjogren’s syndrome.
A negative RF test does not exclude RA or Sjögren’s syndrome. About 20% of patients with RA or Sjögren’s syndrome will be persistently negative or have low levels of RF.
Positive RF test results may also be seen in healthy patients and in patients with conditions such as: infections; viral infection; endocarditis; tuberculosis; syphilis; systemic lupus erythematosus (lupus); sarcoidosis; cancer; or disease of the liver, lung, or kidney. The RF test is not used to diagnose or monitor these conditions.
Is there anything else I should know?
The RF test is not diagnostic or specific for RA or Sjögren’s syndrome. It must be interpreted in conjunction with the patient’s symptoms and history, and with tests of inflammation such as ESR or CRP. The frequency of falsely positive RF results increases with as we get older.
Does a high level of RF mean that my arthritis is bad?
While it is true that high levels of this autoantibody are often found in people with active cases of rheumatoid arthritis, high RF levels may also result from Sjögren’s syndrome or other inflammatory conditions.
Laboratory monitoring in RA usually involves measurement of inflammatory markers ESR & CRP.
Increased RF levels in your blood can also mean that you have infection; viral infection; endocarditis; tuberculosis; syphilis; systemic lupus erythematosus (lupus); sarcoidosis; cancer; or disease of the liver, lung, or kidneys.