At a Glance
Why Get Tested?
To help diagnose rheumatoid arthritis (RA) and Sjögren’s syndrome
When to Get Tested?
When your doctor thinks that you have symptoms suggestive of RA or Sjögren’s syndrome
Sample Required?
A blood sample taken from a vein in your arm
The Test Sample
What is being tested?
This test detects and measures rheumatoid factor (RF), a type of “autoantibody”, in the blood. We all have antibodies (also known as immunoglobulins) in our blood, which are protective proteins which defend the body against infection, particularly from bacteria. However, “autoantibodies” may attack the patient’s own tissues mistakenly identifying them as “foreign”. While the role of RF is not well understood, it may not directly cause joint damage, but promote the body's inflammation reaction which in turn contributes to autoimmune joint destruction.
The RF test is sensitive but not very specific, implying it can be found in diseases other than rheumatoid arthritis (RA). It is most closely associated with RA but may also be present in other autoimmune disorders, such as Sjögren’s syndrome, in some persistent bacterial and viral infections, and can be found in a small percentage of healthy people particularly in the elderly.
How is the sample collected for testing?
A blood sample is collected from a vein in your arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
The Test
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. 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 relatively new test that can help detect early RA may be used if RF is negative, and there is a high suspicion of RA. The RF test may also be requested with other autoantibody tests such as anti-Ro (SS-A) and anti-La (SS-B) which help diagnose Sjögren’s syndrome.
When is it requested?
The test for RF may be requested when a patient has signs of RA. 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.
Common Questions
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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
