What is a rheumatoid factor (RF) test?
A rheumatoid factor (RF) test measures the amount of rheumatoid factor (RF) in your blood. Rheumatoid factors are proteins produced by the immune system. Normally, the immune system attacks disease-causing substances like viruses and bacteria. Rheumatoid factors attack healthy joints, glands, or other normal cells by mistake.
An RF test is most often used to help diagnose rheumatoid arthritis. Rheumatoid arthritis is a type of autoimmune disorder that causes pain, swelling, and stiffness of the joints. Rheumatoid factors may also be a sign of other autoimmune disorders, such as juvenile arthritis, certain infections, and some types of cancer.
Other names: RF Blood Test
What is it used for?
An RF test is used to help diagnose rheumatoid arthritis or other autoimmune disorders.
Why do I need an RF test?
You may need an RF test if you have symptoms of rheumatoid arthritis. These include:
- Joint pain
- Joint stiffness, especially in the morning
- Joint swelling
- Low-grade fever
What happens during an RF test?
A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.
Will I need to do anything to prepare for the test?
You don’t need any special preparations for an RF test.
Are there any risks to the test?
There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.
What do the results mean?
If rheumatoid factor is found in your blood, it may indicate:
- Rheumatoid arthritis
- Another autoimmune disease, such lupus, Sjogren’s syndrome, juvenile arthritis, or scleroderma
- An infection, such as mononucleosis or tuberculosis
- Certain cancers, such as leukemia or multiple myeloma
About 20 percent of people with rheumatoid arthritis have little or no rheumatoid factor in their blood. So even if your results were normal, your health care provider may order more tests to confirm or rule out a diagnosis.
If your results were not normal, it doesn’t necessarily mean you have a medical condition needing treatment. Some healthy people have rheumatoid factor in their blood, but it’s not clear why.
Is there anything else I need to know about an RF test?
An RF test is not used to diagnose osteoarthritis. Although rheumatoid arthritis and osteoarthritis both affect the joints, they are very different diseases. Rheumatoid arthritis is an autoimmune disease that affects people at any age, but usually occurs between the ages of 40 and 60. It affects more women than men. Symptoms may come and go and vary in severity. Osteoarthritis is not an autoimmune disease. It is caused by the wear and tear of joints over time and usually affects adults over the age of 65.