Antinuclear Antibody 

Updated: Sep 04, 2014
  • Author: Asma Al-Zougbi, MD; Chief Editor: Eric B Staros, MD  more...
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Reference Range

Antinuclear antibody (ANA) tests identify antibodies present in serum that bind to autoantigens present in the nuclei of mammalian cells. Most of these antibodies are IgG, but IgM and IgA have also been detected. The enzyme-linked immunosorbent assay (ELISA) method involves the interaction of these antibodies present in the serum sample with a preprepared antigen, and the addition of an antibody that adheres to this complex and induces a color change; the result is an optical density value (a photometric scale) that is read as positive, negative, or equivocal.

The reference range for antinuclear antibody is negative by ELISA.

If the ELISA method results in an abnormal or equivocal finding, the sample is titered using indirect immunofluorescence (IFA) assays on Hep-2 cells, and any value less than or equal to 1:40 dilution (or < 1.0 IU) is negative. [1]

The frequency of positivity on ANA screening test (on Hep-2 cells) is as follows:

  • Mixed connective tissue disease: 100%
  • Drug-induced lupus erythematosus: 100%
  • Systemic lupus erythematosus: 95%-100%
  • Sjögren syndrome: 80%
  • Scleroderma: 60%-95%
  • Polymyositis-dermatomyositis: 49%-74%
  • Rheumatoid arthritis: 40%-60%
  • Normal: Less than 4%
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Interpretation

A negative value indicates that the diagnosis of a connective tissue disease is unlikely.

Any value greater than or equal to 1:160 is significantly positive (in some laboratories, this is reported in international units in which 1 IU is equivalent to 1:160). The degree of clinical positivity is as follows:

  • Less than or equal to I.0 U is negative.
  • 1.1-2.9 U is weakly positive.
  • 3.0-5.9 U is positive.
  • Greater than or equal to 6.0 U is strongly positive.

Different connective tissue diseases are associated with a different frequency of ANA positivity (see the image below). An antibody pattern is reported with a positive titer and gives an indication of the likely diagnosis (see the image below). Pattern interpretation is subjective and thus frequently not specific for any individual disease state.

ANA patterns. ANA patterns.

A positive result does not confirm a disease; rather it compliments clinical signs and symptoms, specific antibody tests, and histopathologic and radiographic findings.

Considerable interlaboratory variability exists in reported titers, with a variation of 1:32 to greater than 1:5120 on the same specimen.

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Collection and Panels

No environmental conditions affect the results of this test.

A 7-mL blood serum sample is collected in a red-topped tube and may be stored at 48 º C for up to 72 hours or at -20 º C or colder (without freezing and thawing) indefinitely. For IFF, acetone-fixed substrate slides are preferred to ethanol and methanol fixation because the latter may remove SSA antigen.

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Background

ANA tests identify antibodies present in serum that bind to autoantigens present in the nuclei of mammalian cells. Most of these antibodies are IgG, but IgM and IgA have also been detected. The ELISA method involves the interaction of these antibodies present in the serum sample with a preprepared antigen and the addition of an antibody that adheres to this complex and induces a color change; the result is an optical density value (a photometric scale) that is read as positive, negative, or equivocal.

The IFA method used in most laboratories uses human tumor cell-line substrate (the HEp-2 cell line) to detect the presence of these antibodies in human serum. A fluorescent-labeled antibody adheres to this antigen-antibody complex and allows visualization of the pattern. Any pattern visualized at a 1:40 dilution should be titered to end dilution (ie, the first dilution at which pattern can no longer be visualized). [2, 3, 4]

ANA is the screening method of choice for systemic rheumatic diseases (as sometimes referred to as connective tissue or collagen diseases) such as systemic lupus erthyematosus (SLE), mixed connective tissue disease, Sjögren syndrome, scleroderma, CREST syndrome, rheumatoid arthritis, polymyositis, and dermatomyositis. [5]

Drugs (ie, procainamide, phenytoin, penicillin, and hydralazine), neoplasms, chronic liver disease, viral illnesses, and chronic infections may result in low titers of ANAs. Elderly and otherwise healthy persons may also have low titers.

Patients with SLE receiving steroids may have negative test results. Some patients with SLE may have a negative ANA test.

No conditions exist under which this test should not be performed.

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