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.