In autoimmune disorders, the immune system mistakenly recognizes a natural body constituent as "foreign" and begins to attack healthy cells, causing tissue destruction. This immune attackwhich may be generalized and take place in a number of tissues, or may focus on a single organis executed by substances called autoantibodies, which target specific components of cells such as the nucleus or cell receptors. Blood tests for the following autoantibodies are often performed to aid in the diagnosis of autoimmune disorders:
Antinuclear antibody is present in almost all people with systemic lupus erythematosus (SLE)a generalized autoimmune condition that attacks a number of different tissues. It is also found in some individuals with rheumatoid arthritis, scleroderma (which destroys connective tissue), Sjögren's syndrome (which causes dry mouth and eyes), polymyositis (which affects the nerves and muscles), and certain forms of chronic active hepatitis (a nonautoimmune liver disease).
Anti-DNA antibody may be found in people with SLE, but is typically not present in other autoimmune diseases.
Antiphospholipid antibody, which is associated with blood clot formation and miscarriages, may be present in SLE and certain other autoimmune conditions.
Anti-smooth muscle antibody, frequently present in patients with chronic active hepatitis, aids in distinguishing between this and other forms of liver disease.
Antimitochondrial antibody is present in most patients with primary biliary cirrhosis (an autoimmune liver disorder) and is found rarely in other types of chronic liver disease.
Acetylcholine receptor antibodies—which are present in the majority of patients with myasthenia gravis (an autoimmune disorder affecting the nerves and muscles)—are tested to aid in the diagnosis of this disease, and also to help monitor the effectiveness of immunosuppressive therapy for the condition.
Purpose of the Antibody Tests for Autoimmune Disorders
- To document infectious/foreign agent
- To know how protected you are against a microorganism (immune status)
- To assist in the diagnosis of autoimmune disorders
- To monitor the course and treatment of an autoimmune disorder
Who Performs Antibody Tests
- A doctor, a nurse, or a lab technician
Special Concerns about Antibody Tests
- False-positive and false-negative results are possible.
- Certain medications may alter the results of some of these tests.
- A radioactive scan performed within 1 week before the anti-DNA antibody test may alter the results of this test.
- Antinuclear antibodies may be found in the blood of healthy older people and occasionally in some healthy younger individuals.
Before the Antibody Tests for Autoimmune Disorders
- Report to your doctor any medications you are taking. You may be advised to discontinue certain of these agents before the test.
What You Experience
- A sample of your blood is drawn from a vein, usually in your arm, and sent to a laboratory for analysis.
Risks and Complications of Antibody Tests
- There are no known risks or complications.
After the Antibody Tests for Autoimmune Disorders
- Immediately after blood is drawn, pressure is applied (with cotton or gauze) to the puncture site.
- Resume your normal diet and any medications withheld before the test.
- Blood may collect and clot under the skin (hematoma) at the puncture site; this is harmless and will resolve on its own. For a large hematoma that causes swelling and discomfort, apply ice initially; after 24 hours, use warm, moist compresses to help dissolve the clotted blood.
Antibody Test Results
- Your blood sample is sent to a laboratory and analyzed for the presence of autoantibodies. Your doctor will review the test results in conjunction with your symptoms, medical history, and physical exam for evidence of an autoimmune disorder.
- If results are positive and your doctor can make a definitive diagnosis, appropriate therapy will begin.
- In many cases, one or more positive results on these blood tests will necessitate additional procedures—for example, a biopsy of the lip, liver, or muscle—to confirm a diagnosis.
- The absence of autoantibodies suggests you may have a condition other than an autoimmune disorder, and other tests may be scheduled.
The Johns Hopkins Consumer Guide to Medical Tests
Simeon Margolis, M.D., Ph.D., Medical Editor
Updated by Remedy Health Media