ANA
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Also known as: Antinuclear Antibody; Fluorescent Antinuclear Antibody; FANA
Formal name: Antinuclear Antibody
The Test
How is it used?
When is it ordered?
What does the test result mean?
Is there anything else I should know?
How is it used?
The antinuclear antibody (ANA) test is ordered to help screen for autoimmune disorders and is most often used as one of the tests to diagnose systemic lupus erythematosus (SLE). Depending on the person's symptoms and the suspected diagnosis, ANA may be ordered along with one or more other autoantibody tests. Other laboratory tests associated with presence of inflammation, such as erythrocyte sedimentation rate (ESR) and/or C-reactive protein (CRP), may also be ordered. ANA may be followed by additional tests that are considered subsets of the general ANA test and that are used in conjunction with the person's clinical history to help rule out a diagnosis of other autoimmune disorders.
When is it ordered?
The ANA test is ordered when someone shows signs and symptoms that are associated with SLE or another autoimmune disorder. It may also be ordered when a person has been diagnosed with an autoimmune disorder and the doctor suspects that she may have developed an additional autoimmune disorder. Those with autoimmune disorders can have a wide variety of symptoms such as low-grade fever, joint pain, fatigue, and/or unexplained rashes that may change over time.
What does the test result mean?
ANA tests are performed using different assays (indirect immunofluorescence microscopy or by enzyme-linked immunoabsorbant assay, ELISA) and results are reported as a titer, often with a particular type of immunofluroscence pattern (when positive). Low-level titers are considered negative, while increased titers, such as 1:320, are positive, indicating an elevated concentration of antinuclear antibodies.
ANA shows up on indirect immunofluorescence as fluorescent patterns in cells that are fixed to a slide that is evaluated under a microscope. Different patterns have been associated with a variety of autoimmune disorders, although overlap may occur. Some of the more common patterns include:
Homogenous (diffuse) - associated with SLE and mixed connective tissue disease
Speckled - associated with SLE, Sjogren syndrome, scleroderma, polymyositis, rheumatoid arthritis, and mixed connective tissue disease
Nucleolar - associated with scleroderma and polymyositis
Centromere pattern (peripheral) - associated with scleroderma and CREST (Calcinosis, Raynaud's syndrome, Esophogeal dysmotility, Sclerodactyly, Telangiectasia)
An example of a positive result might be: "Positive at 1:320 dilution with a homogenous pattern."
A positive ANA test result may suggest an autoimmune disease, but further specific testing is required to assist in making a final diagnosis. ANA test results can be positive in people without any known autoimmune disease. While this is not common, the frequency of a false positive ANA result increases as people get older.
Also, ANA may become positive before signs and symptoms of an autoimmune disease develop, so it may take time to tell the meaning of a positive ANA in a person who does not have symptoms. Most positive ANA results don't have significance, so physicians should reassure their patients but should also still be vigilant for development of signs and symptoms that might suggest an autoimmune disease.
About 95% of those with SLE have a positive ANA test result. If someone also has symptoms of SLE, such as arthritis, a rash, and autoimmune thrombocytopenia, then she probably has SLE. In cases such as these, a positive ANA result can be useful to support SLE diagnosis. Two subset tests for specific types of autoantibodies, such as anti-dsDNA and anti-SM, may be ordered (often as an ENA panel) to help confirm that the condition is SLE.
A positive ANA can also mean that the person has drug-induced lupus. This condition is associated with the development of autoantibodies to histones, which are water-soluble proteins rich in the amino acids lysine and arginine. An anti-histone test may be ordered to support the diagnosis of drug-induced lupus.
Other conditions in which a positive ANA test result may be seen include:
Sjögren syndrome: Between 40% and 70% of those with this condition have a positive ANA test result. While this finding supports the diagnosis, a negative result does not rule it out. The doctor may want to test for two subsets of ANA: Anti-SS-A (Ro) and Anti-SS-B (La). About 90% or more of people with Sjögren syndrome have autoantibodies to SSA.
Scleroderma (systemic sclerosis): About 60% to 90% of those with scleroderma have a positive ANA finding. In people who may have this condition, ANA subset tests can help distinguished two forms of the disease, limited versus diffuse. The diffuse form is more severe. Limited disease is most closely associated with the anticentromere pattern of ANA staining (and the anticentromere test), while the diffuse form is associated with autoantibodies to the anti–Scl-70.
A positive result on the ANA also may show up in people with Raynaud's disease, rheumatoid arthritis, dermatomyositis or polymyosis, mixed connective tissue disease, and other autoimmune conditions. For more on these conditions, visit the American Autoimmune Related Diseases Association patient information page.
A doctor must rely on test results, clinical symptoms, and the person's history for diagnosis. Because symptoms may come and go, it may take months or years to show a pattern that might suggest SLE or any of the other autoimmune diseases.
A negative ANA result makes SLE an unlikely diagnosis. It usually is not necessary to immediately repeat a negative ANA test; however, due to the episodic nature of autoimmune diseases, it may be worthwhile to repeat the ANA test at a future date if symptoms persist.
Aside from rare cases, further autoantibody (subset) testing is not necessary if a person has a negative ANA result.
Is there anything else I should know?
A number of drugs and some infections (such as chronic non-viral hepatitis, primary biliary cirrhosis) as well as other conditions mentioned above can give a false positive result for the ANA test.
About 3% - 5% of Caucasians may be positive for ANA and it may reach as high as 10% - 37% in healthy individuals over the age of 65.
A number of medications may bring on a condition that includes SLE symptoms, called drug-induced lupus. When the drugs are stopped, the symptoms usually go away. Although many medications have been reported to cause drug-induced lupus, those most closely associated with this syndrome include hydralazine, isoniazid, procainamide, and several anticonvulsants.
Though some laboratories may use an immunoassay to test for ANA, indirect fluorescent antibody (IFA) is still considered the gold standard. Often, laboratories will screen using immunoassay and confirm positive or equivocal results using IFA.
http://labtestsonline.org/understanding/analytes/ana/tab/test
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