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The immune system makes an abundance of proteins called antibodies. Antibodies are made by white blood cells (B cells). The antibodies recognize and combat infectious organisms (germs) in the body. Antibodies develop in our immune system to help the body fight infectious organisms. When an antibody recognizes the foreign proteins of an infectious organism, it recruits other proteins and cells to fight off the infection. This cascade of attack is called inflammation.
Sometimes these antibodies make a mistake, identifying normal, naturally-occurring proteins in our bodies as being “foreign” and dangerous. When these antibodies make incorrect calls, identifying a naturally-occurring protein (or self protein) as foreign, they are called autoantibodies. Autoantibodies start the cascade of inflammation, causing the body to attack itself. The antibodies that target “normal” proteins within the nucleus of a cell are called antinuclear antibodies (ANA). Most of us have autoantibodies, but typically in small amounts. The presence of large amount of autoantibodies or ANAs can indicate an autoimmune disease. ANAs could signal the body to begin attacking itself which can lead to autoimmune diseases, including lupus, scleroderma, Sjögren’s syndrome, polymyositis/dermatomyositis, mixed connective tissue disease, drug-induced lupus, and autoimmune hepatitis. A positive ANA can also be seen in juvenile arthritis.
There are several methods used to test for ANAs. One method is a blood test called the Fluorescent Antinuclear Antibody Test or FANA. This test involves viewing fluorescent-labeled antibodies on a glass side under the microscope and determining the pattern and intensity of the fluorescence.
The sensitivity and simplicity of an ANA test makes it extremely popular to screen for lupus in particular. Since most people (more than 95 percent of individuals) with lupus will test positive, a negative ANA test can be helpful in excluding that diagnosis. That said, only about 11-13 percent of persons with a positive ANA test have lupus and up to 15 percent of completely healthy people have a positive ANA test. Thus a positive ANA test does not automatically translate into a diagnosis of lupus or any autoimmune or connective tissue disease.
FANA test results are reported in titers and the patterns that the autoantibodies make, e.g., homogeneous, speckled, centromere, etc. This titer reading is determined by adding saline (salt water) to the liquid portion of a person’s blood.
For example, 1 part blood is mixed with 40 parts saline to create a 1:40 dilution. The dilution then is taken through a series of additional steps, creating tubes of 1:80, 1:160, 1:320, and 1:640 dilutions, respectively.
A negative ANA reading means no autoantibodies are present in the body. However, a positive ANA reading alone does not indicate an autoimmune disease.
The positive ANA reading simply tells your doctor to keep looking. In fact, you may have a “false positive” ANA, which means that the evidence is not there to make a diagnosis of lupus or any other autoimmune disease. To make a definite diagnosis, your doctor will need more blood tests along with history of your symptoms and a physical examination.
Your rheumatologist will interpret your ANA in the context of other laboratory studies and your clinical history, including family history. Remember, a single positive ANA does not imply autoimmune disease, nor does a positive ANA require immediate treatment. Lab levels vary; some autoantibodies are normal; and this may be a false positive result.
Your doctor will determine what happens next based on additional exploration. By working with your doctor and asking questions you will get the best care for your particular situation. Keep in mind, even if your ANA reading does lead to an autoimmune diagnosis, there are treatments for all autoimmune diseases.
Updated June 2015. Written by Joan Marie Von Feldt, MD, MSEd and reviewed by the American College of Rheumatology Committee on Communications and Marketing.
This information is provided for general education only. Individuals should consult a qualified health care provider for professional medical advice, diagnosis and treatment of a medical or health condition.
©2015 American College of Rheumatology