Rheumatoid arthritis (RA) is characterized by chronic inflammation of joints. It is an autoimmune disease that is caused when the immune system starts attacking the body's own tissues by mistake. Diagnosis of this disease is done by detecting the antibody rheumatoid factor (RF), which is present in the blood of around 80% of the patients. There is a rheumatoid factor range that determines whether a person has this disease or not.
What Is Normal Rheumatoid Factor Range?
The rheumatoid factor (RF) blood test measures the level of the RF antibody in the blood. There are two ways in which the normal rheumatoid factor range can be presented.
- Titer: Below 1:80 (1 to 80) titer
- Units: Below 40-60 units per milliliter (U/Ml)
Notes:
A titer is a measure of the dilution of blood after which the detection of RF is no longer possible. A titer of 1:20 (1 to 20) indicates that RF is detectable when 1 part of sample of blood is diluted to up to 20 parts of saline. The larger the second number, the more the RF presence in blood.
Nephelometry units show the amount of light that is blocked by the sample of blood present in the tube. High levels of RF make the samples cloudy, allowing less light to pass through than when the levels are low.
Each lab has a different rheumatoid factor range and it is possible that your lab has a different normal range. The range used by your lab will be written in your lab report. The results are evaluated by the doctors on the basis of your health and many other factors. Therefore, your values might still be normal even if they fall outside the range mentioned here.
What If Having High Values?
Getting a positive test result means that the levels of rheumatoid factor found in your blood are higher than the normal rheumatoid factor range. It may be the first indication that you might be suffering from rheumatoid arthritis.
Sjogren syndrome and rheumatoid arthritis patients usually have positive RF tests. High levels of RF increase the likelihood of presence of RA or Sjogren syndrome. Diagnosis of these disorders can be done by other tests. However, not all people having a high level of RF have Sjogren syndrome or rheumatoid arthritis. Confirmation of the diagnosis of rheumatoid arthritis may be done by doing blood test for anti-CCP antibody.
High levels of RF are also present in people suffering from the following diseases:
- Sarcoidosis
- Dermatomyositis
- Adult Still's disease
- Systemic lupus erythematosus
- Scleroderma
Levels of RF that are higher than the normal rheumatoid factor range are found in patients suffering from other medical problems too, for example:
- Chronic lung or liver disease
- Multiple myeloma, leukemia and other cancers
- Parasite infections
- Tuberculosis, Endocarditis and other bacterial infections
- Some kidney diseases
- Infectious mononucleosis, influenza, hepatitis, AIDS and other viral infections
Sometimes healthy people with no medical problems can also have high levels of RF.
When Is Rheumatoid Factor Test Ordered?
Patients with symptoms of RA are usually asked to get this test by doctors. The following are some common symptoms of RA:
- Swelling and warmth in joints
- Stiffness in joints
- Loss of bone
- Cartilage loss
- Nodules growths under the skin
- Elevated pain in joints in morning
The RF test is also ordered by doctors for diagnosing Sjogren's syndrome. It is a condition in which the white blood cells start attacking the moisture-secreting glands and mucous membranes of the mouth and eyes. Muscle and joint pain, extreme fatigue and dry eyes and mouth are the primary symptoms of this disease.
How Is Rheumatoid Factor Test Performed?
The RF test is just like an ordinary blood test. The test is performed by drawing blood from the patient's arm. It takes only a few minutes to draw the blood and involves the following procedure:
- First, the skin over the vein is cleaned.
- The vein is allowed to fill up with blood by securing an elastic band around the arm after which a small needle is carefully inserted.
- A sterile vial is used for collecting blood which is then sent to the laboratory for RF antibody testing.
- Covering of the puncture site is done using gauze and adhesive bandage after the blood has been drawn.