Rheumatoid Factor (RF)
A blood sample drawn from a vein in your arm
Rheumatoid factor (RF) is an autoantibody, an immunoglobulin M (IgM) protein that is produced by the body's immune system. Autoantibodies attack a person's own tissues, mistakenly identifying the tissue as "foreign." While the biologic role of RF is not well understood, its presence is useful as an indicator of inflammatory and autoimmune activity. This test detects and measures RF in the blood.
The RF test is a valuable test for helping to diagnose rheumatoid arthritis (RA). About 80% of those with RA will have a positive RF test. However, RF may also be detected in people with a variety of other disorders, including other autoimmune disorders such as Sjögren syndrome, as well as persistent bacterial, viral, and parasitic infections, and certain cancers. It may sometimes be seen in those with lung disease, liver disease, and kidney disease, and it can be found in a small percentage (1-5%) of healthy people.
How is it used?
While diagnosis of RA relies heavily on the clinical picture, some of the signs and symptoms may not be present or follow a typical pattern, especially early in the disease. Furthermore, the signs and symptoms may not always be clearly identifiable since people with RA may also have other connective tissue disorders or conditions, such as Raynaud phenomenon, scleroderma, autoimmune thyroid disorders, and systemic lupus erythematosis, and display symptoms of these disorders as well. The RF test is one tool among others that can be used to help make a diagnosis when RA is suspected.
When is it ordered?
The test for RF may be ordered when a person has signs and symptoms 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.
A cyclic citrullinated peptide (CCP) antibody test can help diagnose RA in someone who has joint inflammation with symptoms that suggest but do not yet meet the criteria of RA and may be ordered along with RF or if the RF result is negative.
The RF test may also be ordered along with other autoimmune-related tests, such as an antinuclear antibody (ANA), and other markers of inflammation, such as a C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR), as well as a complete blood count (CBC) to evaluate blood cells.
What does the test result mean?
The RF test must be interpreted in conjunction with a person's symptoms and clinical history.
In those with symptoms and clinical signs of rheumatoid arthritis, the presence of significant concentrations of RF indicates that it is likely that they have RA. Higher levels of RF generally correlate with more severe disease and a poorer prognosis.
A negative RF test does not rule out RA. About 20% of people with RA will have very low levels of or no detectable RF. In these cases, a CCP antibody test may be positive and used to confirm RA.
Positive RF test results may also be seen in 1-5% of healthy people and in some people with conditions such as: Sjögren syndrome, scleroderma, systemic lupus erythematosus (lupus), sarcoidosis, endocarditis, tuberculosis, syphilis, HIV/AIDS, hepatitis, infectious mononucleosis, cancers such as leukemia and multiple myeloma, parasitic infection, or disease of the liver, lung, or kidney. The RF test is not used to diagnose or monitor these other conditions.
Is there anything else I should know?
The 2010 Rheumatoid Arthritis Classification Criteria from the American College of Rheumatology (ACR) includes cyclic citrullinated peptide (CCP) antibody testing, along with RF, as part of its criteria for diagnosing rheumatoid arthritis. According to the ACR, CCP antibodies may be detected in about 50-60% of people with early RA, as early as 3-6 months after the beginning of symptoms. Early detection and diagnosis of RA allows health practitioners to begin aggressive treatment of the condition, minimizing the associated complications and tissue damage.
Does everyone need an RF test?
Can an RF test be performed in my doctor's office?It could be performed in your doctor's office, but in most cases the test will be sent to the laboratory.