How is it used?
The antinuclear antibody (ANA) test is used as a primary test to help evaluate a person for autoimmune disorders that affect many tissues and organs throughout the body (systemic) and is most often used as one of the tests to help diagnose systemic lupus erythematosus (SLE).
ANA are a group of autoantibodies produced by a person's immune system when it fails to adequately distinguish between "self" and "nonself." They target substances found in the nucleus of a cell and cause organ and tissue damage.
Depending on a person's signs and symptoms and the suspected disorder, ANA testing may be used along with or followed by other autoantibody tests. Some of these tests are considered subsets of the general ANA test and detect the presence of autoantibodies that target specific substances within cell nuclei, including anti-dsDNA, anti-centromere, anti-nucleolar, anti-histone and anti-RNA antibodies. An ENA panel may also be used in follow up to an ANA.
These supplemental tests are used in conjunction with a person's clinical history to help diagnose or rule out other autoimmune disorders, such as Sjögren syndrome, polymyositis and scleroderma.
Different laboratories may use different test methods to detect ANA. Two common methods include immunoassay and indirect fluorescent antibody (IFA). IFA is considered the gold standard. Some laboratories will use immunoassay to screen for ANA and use IFA to confirm positive or equivocal results.
- Indirect fluorescent antibody (IFA)—this is a method in which a person's blood sample is mixed with cells that are affixed to a slide. Autoantibodies that may be present in the blood react with the cells. The slide is treated with a fluorescent antibody reagent and examined under a microscope. The presence (or absence) and pattern of fluorescence is noted.
- Immunoassays--these methods are usually performed on automated instrumentation but may be less sensitive than IFA in detecting ANA.
Other laboratory tests associated with the presence of inflammation, such as erythrocyte sedimentation rate (ESR) and/or C-reactive protein (CRP), may also be used to evaluate a person for SLE or other autoimmune disese.
When is it ordered?
The ANA test is ordered when someone shows signs and symptoms that are associated with a systemic autoimmune disorder. People with autoimmune disorders can have a variety of symptoms that are vague and non-specific and that change over time, progressively worsen, or alternate between periods of flare ups and remissions. Some examples of signs and symptoms include:
- Low-grade fever
- Persistent fatigue, weakness
- Arthritis-like pain in one or more joints
- Red rash (for lupus, one resembling a butterfly across the nose and cheeks)
- Skin sensitivity to light
- Hair loss
- Muscle pain
- Numbness or tingling in the hands or feet
- Inflammation and damage to organs and tissues, including the kidneys, lungs, heart, lining of the heart, central nervous system, and blood vessels
What does the test result mean?
A positive ANA test result means that autoantibodies are present. In a person with signs and symptoms, this suggests the presence of an autoimmune disease, but further evaluation is required to assist in making a final diagnosis.
Tests for ANA
Amount of autoantibody present
Two types of tests are commonly performed to detect and measure ANA:
- Immunoassay (enzyme linked immunosorbent assay, ELISA, or enzyme immunoassay, EIA)—the results are usually reported as a number with an arbitrary unit of measure (abbreviated as a "U" on the report, for example).
- Indirect fluorescent antibody (IFA)—the results of this method are reported as a titer. Titers are expressed as ratios. For example, the result 1:320 means that one part blood sample was mixed with 320 parts of a diluting substance and ANA was still detectable.
Patterns of cellular fluorescence
In addition to a titer, positive results on IFA will include a description of the particular type of fluorescent pattern seen. Different patterns have been associated with different autoimmune disorders, although some overlap may occur. Some of the more common patterns include:
- Homogenous (diffuse)—associated with SLE, mixed connective tissue disease, and drug-induced lupus
- Speckled—associated with SLE, Sjögren 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 syndrome, Esophogeal dysmotility, Sclerodactyly, Telangiectasia)
A positive result from the ELISA or EIA method will be a number of units that is above the laboratory's reference number (cutoff) for the lowest possible value that is considered positive.
An example of a positive result using the IFA method would give the dilution titer and a description of the pattern, such as "Positive at 1:320 dilution with a homogenous pattern."
For either method, the higher the value reported, the more likely the result is a true positive.
ANA test results can be positive in people without any known autoimmune disease and thus need to be evaluated carefully in conjunction with an individual's signs and symptoms.
An ANA test 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.
Conditions associated with a positive ANA test
The most common condition is SLE.
- SLE—ANA are most commonly seen with SLE. 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 skin sensitivity to light, then the person probably has SLE. A positive anti-dsDNA and anti-SM (often ordered as part of an ENA panel) help confirm that the condition is SLE.
Other conditions in which a positive ANA test result may be seen include:
- Drug-induced lupus—a number of medications may trigger this condition, which is associated with SLE symptoms. 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. Because this condition is associated with the development of autoantibodies to histones, an anti-histone antibody test may be ordered to support the diagnosis.
- Sjögren syndrome—40-70% 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. A health practitioner 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 60-90% of those with scleroderma have a positive ANA. In people who may have this condition, ANA subset tests can help distinguish two forms of the disease, limited versus diffuse. The diffuse form is more severe. The limited form is most closely associated with the anticentromere pattern of ANA staining (and the anticentromere test), while the diffuse form is associated with autoantibodies to Scl-70.
- Less commonly, ANA may occur in people with Raynaud syndrome, arthritis, dermatomyositis or polymyositis, mixed connective tissue disease, and other autoimmune conditions. For more on these, read the article on Autoimmune Diseases.
A health practitioner 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 recur.
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?
ANA testing is not used to track or monitor the clinical course of SLE, thus serial ANA tests for diagnosed patients are not commonly ordered.
Use of a number of drugs, some infections, autoimmune hepatitis and primary biliary cirrhosis as well as other conditions mentioned above can give a positive result for the ANA test.
About 3-5% of healthy Caucasians may be positive for ANA, and it may reach as high as 10-37% in healthy individuals over the age of 65 because ANA frequency increases with age. These would be considered false-positive results because they are not associated with an autoimmune disease. Such instances are more common in women than men.
