What Is an ANA Titer IFA Test?
Autoimmune disorders occur when one's body fails to distinguish its own components from foreign invaders and produces disease-fighting substances, such as antibodies, that target its own healthy tissues. The ANA, or anti-nuclear antibody test, screens for autoimmune diseases and, according to Lab Tests Online, is most often used to help physicians diagnose a specific autoimmune disorder called systemic lupus erythematosus, or SLE.
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Methods
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ANA tests are conducted using one of two methods: an indirect immunoflourescence assay or an enzyme-linked immunosorbent assay. When IFA is used, anti-nuclear antibodies show up as fluorescent patterns in cells that have been fixed to a glass slide and examined under a microscope. According to Lab Tests Online, different patterns have been associated with a variety of autoimmune diseases.
Measurement
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An ANA test result is a titer -- in this case the concentration of antibody in a patient's blood. The Lupus Foundation of America explains that an ANA titer indicates the number of times a person's blood can be diluted before the antibodies can no longer be detected. Low-level titers, such as 1:20, are considered negative, while high titers, such as 1:320, are considered positive.
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Interpretation
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According to the Lupus Foundation of America, there is no universal normal range for ANA titers because the definition of "normal" varies from lab to lab. A positive test by itself is not diagnostic of autoimmune disease; a physician relies on numerous criteria, such as patient symptoms, physical examination and additional blood work, to confirm a diagnosis.
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References
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