Rheumatoid Factor Testing
Rheumatoid Factor Testing
Rheumatoid factor is a type of antibody. Antibodies, also called immunoglobulins, are proteins produced by the body. Antibodies work to clear the body of potentially threatening infections or substances, fighting off various invaders, such as virsues, bacteria, toxins, mold spores, etc.
The body’s immune system is made up of lymphoid organs, including lymph nodes, the bone marrow (located within the center of long bones) and the thymus (located in the chest). These lymphoid organs produce lymphocytes, including T cells and B cells. These lymphocytes circulate within the bloodstream, within the lymph system, and are also positioned in clumps within organs and on mucosal surfaces of the body. When a B cell encounters a foreign invader, it recognized it as foreign by virtue of a chemical identifier on its surface (called an antigen). Once the B cell recognizes an antigen, the B cell gives rise to a large number of plasma cells. These plasma cells are capable of producing antibodies.
Antibodies are made up of units called “chains.” All antibodies are composed of two larger chains (called heavy chains) and two smaller chains (called light chains). The tip of the antibody is referred to as the hypervariable region. This hypervariable region is responsible for unique chemical properties possessed by each antibody that allow a specific antibody to “recognize” and match up to a particular antigen. The combination of an antibody with a specific antigen, creates an antibody-antigen complex, marking the invader as foreign and in need of inactivation or destruction by other immune cells in the body.
The first time an antigen is encountered by the immune system, the body’s response is slow. Time is required in order to activate the machinery necessary to produce the very specific type of antibody necessary to combat that antigen. However, if that particular antigen is encountered in the future, the needed machinery is already available, and antibody production in response to a “familiar” antigen is quite rapid.
One of the important attributes of a healthy, well-functioning immune system rests on its ability to distinguish between “self and “other.” This means that it’s crucial that the antibodies don’t mistakenly identify parts of the body itself as foreign invaders. When this does happen, the body’s immune system attacks the body, damaging and destroying it. Conditions in which this occurs are referred to as autoimmune disorders. One example of an autoimmune disorder is the condition called rheumatoid arthritis or RA. In RA, the lining of the joints (synovium) is mis-recognized by the immune system as foreign, resulting in the immune system creating specific antibodies that repeatedly attack, damage, and destroy the joints’ lining, resulting in the cluster of symptoms that accompany this disease.
Rheumatoid factor belongs to the class of antibodies known as IgM antibodies. IgM antibodies are primarily found in the blood, and comprise about 13% of all antibodies. IgM functions to kill bacteria, and is found in the earlier phases of immune response to bacterial invasion of the bloodstream (bacteremia).
In rheumatoid arthritis, rheumatoid factor is directed against IgG antibodies. IgG antibodies are very common circulating antibodies; in fact, about 80% of all circulating antibodies are IgG. IgG is found in blood and tissue fluids. IgG functions to coat invading particles, marking them so that they can more easily and rapidly be taken up by other types of immune cells. IgG is the predominant antibody cell in the later or secondary phase of the immune response.
When rheumatoid factor encounters IgG, it attaches itself to the IgG, forming an immune complex. This immune complex kicks off a complicated immune cascade, prompting the production and release of a variety of chemicals that ultimately misidentify the synovium as “non-self,” attack the lining, and over time cause tremendous destruction.
Rheumatoid factor testing is usually done when an individual is having symptoms compatible with an autoimmune disorder, particularly rheuumatoid arthritis or Sjogren’s syndrome. Suspicious symptoms include joint stiffness, pain and swelling (especially in the morning), bumps (nodules) under the skin, and/or dry eyes, mouth, and skin.
Rheumatoid factor testing is not diagnostic. This means that getting a specific result does not definitively confirm the presence of any particular disease. Instead, the test is used to correlate with the clinical
Antibody— A protein that the body produces in response to exposure to a foreign invader such as a virus, bacteria, fungus, or allergen.
Antigen— The protein marker that prompts the body’s immune system to produce antibodies.
Autoimmune disorder— A condition in which the body produces antibodies that serve to attack organs or tissues of the body itself.
Immune system— The collection of organs, tissues, and cells that serve to protect the body against foreign invaders, such as bacteria, viruses, and fungi.
Lymphocyte— A white blood cell; part of the immune system responsible for the production of antibodies.
Plasma cell— The specific type of white blood cell that produces antibodies.
Rheumatoid arthritis— A condition in which the immune system damages and destroys the synovial lining of the joints. Red, warm, swollen, stiff joints are a common symptom. Over time, other organ systems may also be affected, including the heart, eyes, lungs, and kidneys.
Sjogren’s syndrome— A disease in which the immune system damages and destroys exocrine glands, such as those that produce tears and saliva. Dry eyes and mouth are the usual initial symptoms of this disorder, but other organ systems can also be severely affected over time, including the skin, pancreas, liver, lungs, brain, and kidneys.
picture, meaning the history and the symptoms that an individual is experiencing.
Some situations may confuse the results of testing for rheumatoid factor, including very high blood levels of triglycerides or other fats, or advanced age (people over 65 years of age have a higher chance of having a higher-than-normal rheumatoid factor that is not associated with disease).
This test requires blood to be drawn from a vein (usually one in the forearm), generally by a nurse or phlebotomist (an individual who has been trained to draw blood). A tourniquet is applied to the arm above the area where the needle stick will be performed. The site of the needle stick is cleaned with antiseptic, and the needle is inserted. The blood is collected in vacuum tubes. After collection, the needle is withdrawn, and pressure is kept on the blood draw site to stop any bleeding and decrease bruising. A bandage is then applied.
There are no restrictions on diet or physical activity, either before or after the blood test.
As with any blood tests, discomfort, bruising, and/or a very small amount of bleeding is common at the puncture site. Immediately after the needle is withdrawn, it is helpful to put pressure on the puncture site until the bleeding has stopped. This decreases the chance of significant bruising. Warm packs may relieve minor discomfort. Some individuals may feel briefly woozy after a blood test, and they should be encouraged to lie down and rest until they feel better.
Basic blood tests, such as rheumatoid factor testing, do not carry any significant risks, other than slight bruising and the chance of brief dizziness.
Normal rheumatoid factor results would demonstrate a rheumatoid factor titer less than 1:20-1:40, or a rheumatoid factor of less than 43 nephlometry units.
The patient’s, history, symptoms, and rheumatoid factor results are used together in order to arrive at a diagnosis. An elevated rheumatoid factor may indicate the possibility of rheumatoid arthritis or Sjogren’s syndrome. However, some patients (about 20%) with these diseases do not have an elevated rheumatoid factor, or have the condition for several years before their rheumatoid factor becomes abnormally elevated.
Rheumatoid factor may also be elevated in a number of other autoimmune conditions, such as systemic lupus erythematosus, vasculitis, or scleroderma; in severe infections such as syphilis or tuberculosis, mononucleosis, malaria, hepatitis, or endocarditis; in certain types of cancer, including leukemia; and in a number of other conditions, such as cirrhosis of the liver, and lung or kidney disease.
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Harris ED et al. Kelley’s Textbook of Rheumatology. 7th ed. Philadelphia: Saunders, 2005.
McPherson RA et al. Henry’s Clinical Diagnosis and Management By Laboratory Methods. 21st ed. Philadelphia: Saunders, 2007.
American Association of Clinical Chemistry. 1850 K St., N.W., Suite 625, Washington, DC 20006. http://www.aacc.org.
National Institutes of Health. [cited February 10, 2008]. http://www.nlm.nih.gov/medlineplus/encyclopedia.html.
Rosalyn Carson-DeWitt, MD