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.
An RF test is used to help diagnose rheumatoid arthritis or other autoimmune disorders.
You may need an RF test if you have symptoms of rheumatoid arthritis. These include:
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.
You don’t need any special preparations for an RF 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.
If rheumatoid factor is found in your blood, it may indicate:
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.