Rheumatoid Factor (RF) Blood Test
Healthline – Updated for October 2021
Author: Robin Donovan
Medically reviewed by Brenda B. Spriggs, M.D., MPH, FACP
What is rheumatoid factor (RF)?
Rheumatoid factor (RF) is a protein made by your immune system that can attack healthy tissue in your body. Healthy people don’t make RF. So, the presence of RF in your blood can indicate that you have an autoimmune disease.
Sometimes people without any medical problems produce a small amount of RF. That’s very rare, and doctors don’t fully understand why it happens.
Why did my doctor order this test?
Your doctor may order a blood test to check for the presence of RF if they suspect you have an autoimmune condition, such as rheumatoid arthritis or Sjögren syndrome.
Other health problems that can cause higher-than-normal levels of RF include:
- chronic infection
- cirrhosis, which is scarring of the liver
- cryoglobulinemia, which means there are or abnormal proteins in the blood
- dermatomyositis, which is an inflammatory muscle disease
- inflammatory lung disease
- mixed connective tissue disease
Some health problems may cause elevated RF levels, but the presence of this protein alone is not used to diagnose these conditions. These illnesses include:
- viral and parasitic infections
- chronic lung and liver diseases
Why symptoms may prompt an RF test?
Doctors commonly order this test for people who have symptoms of rheumatoid arthritis, which include:
- joint stiffness
- increased joint pain and stiffness in the morning
- nodules under the skin
- a loss of cartilage
- bone loss
- warmth and swelling of the joints
Your doctor may also order tests to diagnose Sjögren syndrome, a condition in which your white blood cells attack the mucous membranes and moisture-secreting glands of your eyes and mouth.
The symptoms of this chronic autoimmune condition are primarily dry mouth and eyes, but they can also include extreme fatigue and joint and muscle pain.
Sjögren syndrome primarily occurs in women and sometimes appears with other autoimmune conditions, including rheumatoid arthritis.
What will happen during the test?
The RF test is a simple blood test. During the test, a healthcare provider draws blood from a vein in your arm or the back of your hand. The blood draw only takes a few minutes. For it, the provider will:
- lean the skin over your vein
- tie an elastic band around your arm so the vein fills quickly with blood
- insert a small needle into the vein
- collect your blood in a sterile vial attached to the needle
- cover the puncture site with gauze and an adhesive bandage to stop any bleeding
- send your blood sample to a lab to be tested for the RF antibody
Risks of a rheumatoid factor test
Test complications are rare, but any of the following may occur at the puncture site:
You have a small risk of developing an infection any time your skin is punctured. To avoid this, keep the puncture site clean and dry.
There’s also a small risk of lightheadedness, dizziness, or fainting during the blood draw. If you feel unsteady or dizzy after the test, be sure to tell the healthcare staff.
Because each person’s veins are a different size, some people may have an easier time with blood draws than others. If it’s difficult for the healthcare provider to access your veins, you may have a slightly higher risk of the minor complications noted above.
You may feel mild to moderate pain during the test.
This is a low-cost test that poses no serious risks to your health.
What do my results mean?
The results of your test are reported as a titer, which is a measurement of how much your blood can be diluted before RF antibodies are undetectable. In the titer method, a ratio of less than 1:80 is considered normal, or less than 60 units of RF per milliliter of blood.
A positive test means that RF is present in your blood. A positive test can be found in 80 percent of people with rheumatoid arthritis. The titer level of the RF typically indicates the severity of the disease, and RF can also be seen in other immune diseases such as lupus and Sjögren’s.
Several studies report a decrease in RF titer in patients treated with certain disease-modifying agents. Other laboratory tests, such as erythrocyte sedimentation rate and C-reactive protein test, can be used to monitor the activity of your disease.
Remember that a positive test doesn’t automatically mean you have rheumatoid arthritis. Your doctor will take into account the results of this test, the results of any other tests you’ve had, and, more importantly, your symptoms and clinical examination to determine a diagnosis.