Rheumatoid factors are proteins produced by your immune system that can attack healthy tissue in your body. Healthy individuals normally do not produce rheumatoid factor, so its presence 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 he or she suspects you have an autoimmune condition, such as rheumatoid arthritis or Sjögren’s syndrome.
According to the Mayo Clinic, other illnesses that can cause higher-than-normal levels of rheumatoid factor include:
- chronic infection
- cirrhosis (scarring of the liver)
- cryoglobulinemia (abnormal proteins in the blood)
- dermatomyositis (an inflammatory muscle disease)
- inflammatory lung disease
- mixed connective tissue disease
Some illnesses, such as HIV/AIDS, hepatitis, the flu, viral and parasitic infections, chronic lung and liver diseases, and leukemia may cause elevated rheumatoid factor levels, but cannot be diagnosed using this blood test alone.
Less commonly, people without any medical problems may produce a small amount of rheumatoid factor. Doctors do not fully understand why.
Physicians commonly order this test for patients who have symptoms of rheumatoid arthritis. Symptoms of this disease include:
- joint stiffness
- increased joint pain in the morning
- nodules under the skin
- loss of cartilage
- bone loss
- warmth and swelling in the joints
Your physician may also order the test to diagnose Sjögren’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 can also include extreme fatigue and joint and muscle pain.
Sjögren’s primarily occurs in women and sometimes appears with other autoimmune diseases, including rheumatoid arthritis.
The rheumatoid factor test is a simple blood test. During the test, a nurse will draw blood from a vein in your arm or the back of your hand. The blood draw will only take a few minutes and will entail the following:
- First, the nurse will clean the skin over your vein.
- An elastic band secured around your arm will allow the vein to fill with blood before the nurse carefully inserts a small needle.
- Blood will collect in a sterile vial attached to the needle and will be sent to a laboratory to be tested for the rheumatoid factor antibody.
- After the blood is drawn, the puncture site will be covered with gauze and an adhesive bandage.
Test complications are rare, but may include pain, bleeding, bruising, or infection at the puncture site. Any time your skin is broken, you have a small risk of developing an infection. To avoid this, keep the puncture site clean and dry. There is 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 nurse.
Because vein size varies from person to person, some people may have an easier time with blood draws than others. If it is 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.
The test is low-cost and poses no serious risks to your health.
The results of your test can be determined using a titer, a measurement of how much your blood can be diluted before rheumatoid factor antibodies are undetectable. In the titer method, a ratio of less than 1:80 is considered normal, or less than 60 U/ml (units of rheumatoid factor per milliliter of blood).
A positive test means that your rheumatoid factor levels are high, which is an indicator of rheumatoid arthritis or Sjogren’s syndrome. The rheumatoid factor test may be ordered on a repeated basis to help monitor the severity of rheumatoid arthritis or Sjogren’s syndrome. Your physician can help you understand your test.
Remember that a positive test does not automatically mean you have rheumatoid arthritis. Your medical team 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.