Rheumatoid Factor (Blood)
Does this test have other names?
RF blood test
What is this test?
This test measures the level of a substance called rheumatoid factor (RF) in your
blood. It helps your healthcare provider find out whether you have rheumatoid arthritis
RF is an autoantibody that responds to inflammation caused by RA. Antibodies increase
in your blood when they find a foreign substance, such as bacteria. Autoantibodies,
on the other hand, attack your own body's proteins.
RF is linked to long-term (chronic) inflammation. So it may be higher if you have
RA, which is an inflammatory condition. Although this autoantibody does not directly
cause arthritis, it plays a role in increasing inflammation if you have joint damage.
RF is found in the blood of 70% to 80% of people with RA.
This test may also help diagnose other rheumatic diseases, chronic infections, or
autoimmune diseases, such as Sjögren's syndrome or lupus erythematosus..
Why do I need this test?
You may need this test if your healthcare provider suspects that you have RA. Symptoms
of RA include:
Arthritis pain often affects finger and toe joints. The knees and shoulders may also
be affected by RA.
If RA is not treated, it can severely affect your daily life and can make it hard
to walk. It's important to start treatment early on. It can be hard to know the problem
is RA and not other inflammatory illnesses, such as polyarthritis. Women are 3 times
more likely than men to have RA. Infections and cigarette smoking may increase the
pain of existing RA.
Long-term effects of RA include damage to your cartilage and bones and decreased function
in your joints.
What other tests might I have along with this test?
Your healthcare provider may order other blood tests to help diagnose RA. These include:
Anti-citrullinated peptide/protein antibody test
Antinuclear antibody, or ANA, testing
Complete blood count, or CBC
Your provider may also order X-rays of your wrists, hands, and feet to look for joint
What do my test results mean?
Many things may affect your lab test results. These include the method each lab uses
to do the test. Even if your test results are different from the normal value, you
may not have a problem. To learn what the results mean for you, talk with your healthcare
Results are given in units per milliliter (U/mL). If your level is lower than 60 U/mL,
your results are considered negative and you likely don't have RA. Levels above that
may mean that you have RA or another autoimmune disease.
The normal level for an older adult may be slightly higher than 60 U/mL.
How is this test done?
The test requires a blood sample, which is drawn through a needle from a vein in your
Does this test pose any risks?
Taking a blood sample with a needle carries risks that include bleeding, infection,
bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight
stinging sensation or pain. Afterward, the site may be slightly sore.
What might affect my test results?
Certain infections can raise your level of RF.
How do I get ready for this test?
You don't need to prepare for this test.