Rheumatoid factor (RF) is a protein produced by your immune system that can attack healthy tissue in your body. Healthy individuals normally don’t produce RF, so the presence of RF in your blood can indicate that you have an autoimmune disease. Your doctor may order a blood test to check for the presence of this protein if they suspect you have an autoimmune condition, such as rheumatoid arthritis or Sjogren’s syndrome.
Other illnesses that can cause higher-than-normal levels of RF include:
- chronic infection
- cirrhosis, or scarring of the liver
- cryoglobulinemia, or abnormal proteins in the blood
- dermatomyositis, which is an inflammatory muscle disease
- inflammatory lung disease
- mixed connective tissue disease
Some illnesses may cause elevated RF levels but cannot be diagnosed using this blood test alone. These illnesses include:
- viral and parasitic infections
- chronic lung and liver diseases
Sometimes people without any medical problems produce a small amount of RF. This is very rare, and doctors don’t fully understand why this happens.
Doctors commonly order this test for people who have symptoms of rheumatoid arthritis. The symptoms of this disease include:
- joint stiffness
- increased joint pain in the morning
- nodules under the skin
- a loss of cartilage
- bone loss
- warmth and swelling in the joints
Your doctor may also order tests to diagnose Sjogren’s 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 disease are primarily dry mouth and eyes, but they can also include extreme fatigue and joint and muscle pain.
Sjogren’s syndrome primarily occurs in women and sometimes appears with other autoimmune diseases, including rheumatoid arthritis.
The RF test is a simple blood test. During the test, a healthcare provider will draw your blood from a vein in your arm or the back of your hand. The blood draw will only take a few minutes, and it involves the following steps:
- They’ll clean the skin over your vein.
- They’ll secure an elastic band around your arm to allow the vein to fill with blood
- They’ll insert a small needle.
- They’ll collect your blood in a sterile vial attached to the needle, and they’ll send it to a laboratory to be tested for the RF antibody.
- After your blood is drawn, the healthcare provider will cover the puncture site with gauze and an adhesive bandage.
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 inform the medical staff.
Because vein size varies from person-to-person, some people may have an easier time with blood draws than others. If it’s difficult 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.
The results of your test can be determined using 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 your RF levels are high, which is an indicator of rheumatoid arthritis or Sjogren’s syndrome. The RF test may be ordered repeatedly to help monitor the severity of rheumatoid arthritis or Sjogren’s syndrome. Your doctor can help you understand the results from the test.
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 your symptoms to reach a diagnosis.